If your ASP.NET web request takes a lot of time (doing some background work etc), then you will need to increase the HttpRequest timeout to avoid the request from getting timed out. If the request times out, you will get this error:
Server Error in Application
Request timed out.
You can fix this quickly by adding this attribute inside the <system.Web> section in your web.config;
where 3600 is the time in seconds.