3.1 Why do I get Error message "Unable to Start Debugging" Error Message When You Send Debug HTTP Request?

This problem can occur if there is some error in the web.config file. To resolve this check for the well-formedness of this document.
For more details refer PRB: "Unable to Start Debugging" Error Message When You Send Debug HTTP Request

3.2 Why do I get the error message "Unable to start debugging on the web server..." when I debug?

There is a possibility that there is no web.config file for the project or there is no Execute permission for the project.

If you already have a web.config file, double check it's well-formedness.

If the web.config file is missing, add one to the directory that contains the ASP.NET application. You can copy one from the numerous samples applications available with the framework installation.

Make sure that the following section reads like this:

On the other hand, if your project already has a Web.config file, and the above section is set as specified, follow these steps to set the Execute Permissions property for the project folder:

1. Start Internet Services Manager, and then click the project that you are trying to debug.
2. Right-click the project, and then click Properties.
3. Click the Directory tab.
4. If None is selected in the Execute Permissions list, click Scripts only, and then click Apply

3.3 When I Debug ASP.NET Applications I get error message "Access Is Denied. Check the DCOM Configuration Settings for the Machine Debug Manager"?

You can get this error if you are user who is trying to remotely debug and you are not a member of the Debugger Users group on the Microsoft Internet Information Server (IIS) server. To add the appropriate user to the Debugger Users group, follow these steps on the Web server:

1. From the Windows Start menu, point to Programs, point to Administrative Tools, and then click Computer Management.
2. In the left pane, click to expand the Computer Management, System Tools, and Local Users and Groups nodes.
3. Click Groups, and then double-click Debugger Users.
4. In the Debugger Users Properties dialog box, click Add.
5. In the Select Users or Groups dialog box, select the appropriate user, and then click OK.
6. Click OK to exit the Debugger Users Properties dialog box.
7. Close the Computer Management explorer.

    

3.4 On Trying to Debug an application, by the F5 key I get the error: "Error while trying to run project: Unable to start debugging on the web server. Catastrophic failure"?

This issue occurs if the account that is used to run the ASP.NET Worker process (by default, the ASPNET user account) is not assigned the "Impersonate a client after authentication" user right in the "Local Security Policy" settings. This issue may occur when you install Microsoft Visual Studio .NET after you install Windows 2000 Service Pack 4 (SP4) on the computer. In this situation, the ASPNET account is not assigned the "Impersonate a client after authentication" user right in the "Local Security Policy" settings.To resolve it, please use the method at: To work around the problem, manually assign Impersonate a client after authentication to the IWAM account. To do so, follow these steps:

1. Click Start, point to Programs, point to Administrative Tools, and then click Domain Controller Security Policy.
2. Click Security Settings.
3. Click Local Policies, and then click User Rights Assignment.
4. In the right pane, double-click Impersonate a client after authentication.
5. In the Security Policy Setting window, click Define these policy settings.
6. Click Add, and then click Browse.
7. In the Select Users or Groups window, select the IWAM account name, click Add, and then click OK.
8. Click OK, and then click OK again.
9. To enforce an update of computer policy, type the following command: secedit /refreshpolicy machine_policy /enforce
10. At a command prompt, type iisreset. In case your server is a Domain Controller Refer PRB: "Catastrophic Failure" Error Message When You Try to Debug an ASP.NET Application on Windows 2000 Domain Controller

     

3.5 How to configure my project for debugging ASP Code?

Access the Project properties window.

Select the Configuration Properties for debugging then in right Pane, under the debugger node select true for Enable ASP debugging.

3.6 In Visual Studio .NET, whenever I try to debug my ASP.NET application I'm not able to stop the debugger on my breakpoints. Why?

Your ASP.NET project is not setup for debugging.

1. Open up the project's properties window and set the "Enable ASP.NET Debugging" option.
2. Open up your web.config file and make sure the Compilation tag's debug attribute is set to true.
   <compilation defaultLanguage="vb" debug="true" />
3. Make sure the account you are logged in as and the ASP.NET Worker process is in the local "Debugger Users" group.

• PRB: Visual Studio .NET Debugger Does Not Stop on Breakpoints When You Debug ASP.NET Pages
• INFO: Common Errors When You Debug ASP.NET Applications in Visual Studio .NET

   

3.7 Why do I get error message "Unable to start debugging on the web server. The debugger is not properly installed. Run setup to install or repair the debugger. Would you like to disable future attempts to debug ASP.NET pages for this project ? "?

If someone has run a lockdown or other security tool on the Web server, the DEBUG method may have been removed.
Go into IIS manager to the Web application's properties and Directory >Configuration (button) > Mappings > Application mappings.
Check that for .aspx extensions, you allow GET,HEAD,POST,DEBUG
Of course you need to be a member of the Debuggers group on the remote server. To resolve error

1. Right-click the Project Name in Solution Explorer, and then click Properties.
2. In the left pane of Properties, click to select Configuration Properties.
3. Click to select Debugging.
4. In the right pane, change the value of Enable Unmanged Debugging to True (on the drop-down list).

3.8 How do I debug JavaScript and other script code in my application using Visual Studio .Net?

1) In IE go to Tools/Internet Options.../Advanced Tab and clear the "Disable Script Debugging" check box options.

2) In VS.Net in your project properties dialog, select "Debugging" under "Configuration Properties" and make sure that "Enable ASP.Net Debugging" is turned on.

3) You can then set break points in script code in VS.Net in custom script files or the application aspx file.

4) VS.Net should give you detailed debugging information for variables in the scope just like other high-level languages.

3.9 What are the different exception-handling approaches that can be used in ASP.NET?

• Using try, catch and finally block in the code
• Using the Error event procedures at the Page, Application or Global levels
• Using the Server Object's GetLastError and ClearError methods

3.10 Why do I get error message "Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server connection"?

This error usually indicates that SQLServer (or MSDE) is configured to use Windows Authentication. If you want to use a SQL login, you will need to enable SQL Authentication (mixed mode authentication). For more details refer PRB: ASP/ODBC/SQL Server Error 0x80040E4D "Login Failed for User '(Null)'"

3.11 Why do I get the Error Message "System.OutOfMemoryException: Exception of type System.OutOfMemoryException was thrown."?

It means that the server is out of available memory. You probably have an infinite loop somewhere that's frantically creating large objects, or you forgot to dispose of disposable objects and memory slowly leaked.

3.12 Why do I get the error message "Sql Server does not exists or access denied " whenever I try to access the data on Sql server?

• The ASP.NET worker process doesn't have the correct permissions to connect to or write to the SQL Server database. Either enable impersonation for users, or configure the ASP.NET worker process to run under the SYSTEM account.
• The ASPNET account cannot establish a named pipes connection to the database server. Try using TCP/IP instead of the Named Pipes protocol to connect to the database by adding "Network Library =dbmssocn" in your connection string

• BUG: Named pipes do not work when worker process runs under ASPNET account
• Process and request identity in ASP.NET

3.13 Why do I get error message "It is already opened exclusively by another user, or you need permission to view its data." when I try to open Access mdb?

The ASPNET worker process doesn't have the correct permissions to connect to or write to the Access database.
Either enable impersonation for users or configure the ASP.NET worker process to run under the SYSTEM account. You can also grant read and write permissions for the "Everyone" group on the database and the database folder.

For more details refer

• PRB: Cannot connect to Access database from ASP.NET
• Process and request identity in ASP.NET

3.14 Why do I get the "HTTP 404 - File not found." error message as "The page cannot be found.The page you are looking for might have been removed, had its name changed, or is temporarily unavailable "?

The reason for this error can be

• The requested file has been renamed.
• The requested file has been moved to another location and/or deleted.
• The requested file is temporarily unavailable due to maintenance, upgrades, or other unknown causes.
• The requested file does not exist.
• IIS 6.0: The appropriate Web service extension or MIME type is not enabled.

3.15 When I install the Microsoft .NET Framework 1.1 on a computer that is running Windows XP, and then you start Windows, the Welcome screen appears. This screen prompts me to click your user name to start Windows.Why?

When you install the .NET Framework 1.1, a hidden local user account that is named ASPNET is created. When you start Windows, Windows treats the ASPNET local user account as an additional user account, although the ASPNET user account is hidden. Therefore, the Welcome screen appears and prompts you to click your user name.
For more details refer KB 827072

3.16 Why do I get the error message "System.InvalidOperationException: Application is restarting"?

This problem occurs because of some antivirus applications write back information to the files that they scan. Every time a user changes the Web.config configuration file, the Global.asax file, or the contents of the Bin folder, the application should restart to incorporate these changes. Because antivirus scanning changes cannot be distinguished from the user's file changes, the application restarts when the antivirus software scans these folders.
Note This problem may occur even when no error is returned. If the virus-scanning software triggers change notifications, every change notification is doubled at the very least: one real change notification and an additional change notification from the antivirus software some time later. For more information refer PRB: Random application restarts with "Application is restarting" error in ASP.NET

3.17 How can I see the Trace messages?

For Page Level Tracing specify the Page Directive as

You can view the page on which trace is enabled to true to see the details.
For Application Level Tracing modify web.config as

You can view the Trace at http://<server>/<webApplicationNam>/trace.axd

3.18 I have installed ASP.NET hotfix and I find that Startup Type of the ASP.NET Session State Service is set to Manual.Why?

Microsoft has acknowledged this as a Bug
To set the StartUp Type as desired refer following steps

1. In Control Panel, open Administrative Tools.
2. Click Services. The Services window appears.
3. Expand the Name column so that the complete name of each service appears.
   Note A Startup Type column displays the current Startup Type value for each service.
4. Double-click the ASP.NET State Service service. The ASP.NET State Service Properties window appears.
5. On the General tab, click one of the following options in the Startup type list:
   • Manual
   • Automatic
   • Disabled
6. Click Apply, and then click OK to save your settings.
   In the Services window, notice your changes to the Startup Type in the Startup Type column.

3.19 Why do I get the error message "aspnet_wp.exe (PID: XXXX) was recycled because it was suspected to be in a deadlocked state "?

This problem might occur because ASP.NET limits the number of worker threads and completion port threads that a call can use to execute requests. For more details refer PRB: Contention, poor performance, and deadlocks when you make Web service requests from ASP.NET applications
You could control the deadlock detection by changing machine.config setting in

3.20 How to display errors using Page_Error event of Page Object?

VB.NET

C#

In the Same manner handle the Errors in the Application_Error event in global.asax

3.21 How to redirect the user to the friendly error-handler page when an Application error occurs?

Modify web.config as

The configuration section supports an inner <error> tag that associates HTTP status codes with custom error pages. For example:

For more details refer <customErrors> Element

3.22 How to Enable Remote Debugging on Windows XP Service Pack 2?

To enable remote debugging on Microsoft® Windows® XP SP2 platforms, the Internet Connection Firewall (ICF) must be configured as follows:

• If ICF is in Shielded mode, you will need to perform appropriate actions so that it is no longer in Shielded mode.
• If ICF is on, a few ports need to be opened and permissions must be granted to Microsoft® Visual Studio® and other executables that are involved in the remote debugging.
• If IFC is off, no firewall configuration is necessary.
• In addition, if the user running Visual Studio is not an Administrator on the remote machine, DCOM settings need to be configured.

3.23 Why do I get error message ""Parser Error Message: Access is denied: Source Error: Line xxx : ""?

The actual problem is because of the Microsoft Indexing Services which scans the Temporary ASP.NET Files and while doing so, the system puts a lock on the same.
To resolve this, the following steps need to be carried out:-

1. Start - Settings - Control Panel - Administrative Tools - Computer mangement.
2. Expand the services and applications node and select the Indexing service node.
3. Expand the Indexing Service Node and then select and expand the System Node.
4. Right click on Directories and select new directory. browse the path to the temporary asp.net files c:\winnt\microsoft.net\framework\v1.1.4322\.
5. Select the temporary asp.net files. give ok and then select the "NO" in the Include in index radiobutton.
6. give ok and then stop and start the indexing service.

3.24 Why do I get the error message "A potentially dangerous Request.Form value was detected from the client "?

Sounds like you are running version 1.1 of ASP.NET / .NET Framework, which added a new security feature called request validation. Request validation looks at every request and determines if it could be a possible CSS (Cross Site Scripting) attack. By default Request Validation is on for every page.
If you wish to allow users to post arbitrary HTML to you site you need to turn off request validation: