Symptom:

Shared Services Administration Site cannot be opened.

and two errors logged in Event Viewer.

Event Type:    Error
Event Source:    ASP.NET 2.0.50727.0
Event Category:    None
Event ID:    1088
Description:
Failed to execute request because the App-Domain could not be created. Error: 0x80070005 Access is denied. 

Event Type:    Error
Event Source:    ASP.NET 2.0.50727.0
Event Category:    None
Event ID:    1334
Description:
Failed to initialize the AppDomain:/LM/W3SVC/1937156701/Root

Exception: System.IO.FileLoadException

Message: Could not load file or assembly 'System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. Access is denied.

Troubleshooting:

Checked the ID in IIS, 1937156701 point to Shared Services Administration Site, it is OK.

But the error message “Could not load file or assembly…”, was totally misleading.

Did a ProcMon:

The Security seems normal with properly accounts and permissions.

However, the application pool account of Shared Services Administration Site (SSPAdminPool in this issue) was NOT in the WSS_WPG group!

Resolution:

Add application pool account of Shared Services Administration Site to WSS_WPG group.

Comments:

It is weird that I had installed MOSS 2007 dozens of times. It is first of time that the application pool account was not in the WSS_WPG group.

However, I am happy that this issue was resolved. :)