Hello Ajax family ,,,

i m new to ajax... just trying to use basic update panel in my project for
learning purpose. so I just tried on that is available at asp.net website's
Ajax portion.
I just copied / pasted same code. The interval of TIMER I set is 50000. that
all is working fine.for some time.... but after some time i get this error
in Alert Box.

i cant get it .. where i m missing anything ?? as for 2-3 minutes it works
OK and then start throughing this exception ..................

*Sys.WebForms.PageRequestManagerServerErrorException: An unknown error
occured while processing the request on the server. The status code returned
from the server was: 500*
and some time Error Code : 403

Can anybody help me in this,,,,

Thanks alot
ABDUL