17.6 Principal causes of errors in the Web server and how to handle them
In the event of an error, make sure that there are sufficient system resources and that there has not been any event log information indicating an error in Microsoft Internet Information Services.
If another program whose application security setting is Low (IIS process) or Medium (pooled) is running on the same Microsoft Internet Information Services, the problem might be in that program.
Also, make sure that neither a network error nor an error in Microsoft Internet Information Services has occurred. See 7.8 Settings for using Microsoft Internet Information Services, and check to make sure that the Web server settings are correct.