Today morning, I got the same error in my ASP.Net application as above. I am not getting this error for first time. But the interesting thing is, I solved the error in different way before. I think this problem can be occurs for many reasons. Since I face the problem and spent time to solve this issue, I think it is better to share ideas with others. It may be helpful for those who will get this error in future.
According to http://support.microsoft.com/kb/315158 the problem occurs because of Aspnet_wp.exe fails to start. By default, ASP.NET runs its worker process (Aspnet_wp.exe) with a weak account (the local machine account, which is named ASPNET) to provide a more secure environment. On a domain controller or on a backup domain controller, all user accounts are domain accounts and are not local machine accounts. Therefore, Aspnet_wp.exe fails to start because it cannot find a local account named "localmachinename\ASPNET". To provide a valid user account on the domain controller, you must specify an explicit account in the
1. Check that ‘IUSR_machine’ and ‘IWAM_machine’
1. Stops the IIS and the ASP.NET state services.
2. Deletes and then re-creates the ASPNET account by using a known temporary password.
3. Reregisters ASP.NET. This step creates a new random password for the account and applies default ASP.NET access control settings for the account.
4. Restarts the Microsoft Internet Information Services (IIS) service.