Hi NaVen. See the following
1. If using any Ajax Toolkit/ Update panels? Then set
EnablePartialRendering to false in the ScriptManager for the page, and then it should give you the actual error.
2. In the web.config file, try playing with
maxRequestLength value.
3. In ASP.Net 4.0 applications, add
ValidateRequest="false" on the page and also
add the below tag in web.config file
<httpruntime maxrequestlength="102400" requestvalidationmode="2.0" />
May I know your application version? .Net 2.0/3.5/4.0
Thank you
Vamsi