Today I tried to change the Project Portal Page on my TFS which is based on WSS 2.0 SP2, after deleting some Web Parts I tried to add them again but it redirect me to the ErrorPage.aspx with an exception like this "Invalid postback or callback argument.", I can add web parts to newly created pages but not the main pages which is unghosted page (Modified or installed from a Template), so I searched the web and I found 3 workarounds:
1) Contact the Microsoft Support by Calling them and ask for Post SP2 hotfix mentioned in http://support.microsoft.com/kb/915746 , which I donot want
2) Wait for SP3 of the WSS 2.0 , which I never wait!!!
3) The workaroung which worked for me (and mostly invented by me :D), is just set the ASP.NET 1.1 for all the WSS Virtual Directory, and the Default Web Site (Port 80), but then set the Reports Virtual Directories (Reports & ReportServer) back to ASP.NET 2.0, and run:
stsadm.exe -o upgrade -forceupgrade -url http://YOURSERVER
which located under: "C:Program FilesCommon FilesMicrosoft Sharedweb server extensions60BIN"
Then Restart the IIS, and everything must be as great as it was.