This can happen for several reasons. An error message detailing the cause of this specific request failure can be found in the application event log of the web server. Open the Event Viewer and see the error message reported. Please review this log entry to discover what caused this error.
If the error message reported is:
Aspnet_wp.exe could not be launched because the username and/or password supplied in the processModel section of the config file are invalid.
Then the most likely causes are:
Microsoft .NET Framework is no longer registered correctly.
The Microsoft Internet Information Server memory is corrupted.
The ASP.NET user no longer has access to the Microsoft .NET Framework folder, the application folder, or the Temporary Files folder.
You have recently applied a security patch to IIS.
Your system is a domain controller.
(Advanced) The processModel section of the Machine.config file does not specify AutoGenerate for the password.
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