Me and my colleagues @ ITWorx came across this weird issue on different environments when trying to access the SSP administration site collection.

Symptoms : When we try to navigate to the SSP administration site default page, we receive the error highlighted in red below. However, we were able to access other SSP administrative pages by typing the URL in the browser.
“Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately. 
Parser Error Message: The base type 
‘Microsoft.Office.Server.Internal.UI.SharedServicesAdminDefaultPage’ is not allowed for this page. The type is not registered as safe.”

Resolution: Add the following line to the SafeControls Section in the web.config of the SSP web application.

<SafeControl Assembly=”Microsoft.Office.Server.UI, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c” Namespace=”Microsoft.Office.Server.Internal.UI” TypeName=”*” />

It’s also worth mentioning that my friend Amir ElKady bought me a Pepsi Can for solving him this issue 🙂
Thanks Amir