Summary
There is an ASP.NET HTTP runtime setting that sets a limit on the amount of time a request is allowed to execute before ASP.NET automatically shuts down the request. Actions such as generating a large PDF or running a slow search may be affected by this limit. The default timeout limit is set to 900 seconds
More Information
Modify the HttpRuntime tag in the Web.config file.
To modify the HTTP request timeout
httpRuntime executionTimeout="900"