Nine times out of ten most TFS related Reporting Services 2005 issues can be resolved by resetting everything back to the original settings.  Follows is a guide on how to do excatly that.  Please ensure you back everything up before doing this and it is at your own risk.  Saying that it's vary rare it goes wrong but consider yourselves warned :)

1. Connect to reporting services using the Reporting Services Configuration tool on the application tier entering the name of the server hosting Reporting Services and the database instance name
2.  In “Report Server Virtual Directory” check “Apply Default Settings” then “Apply”
3. In “Report Manager  Virtual Directory” check “Apply Default Settings” then “Apply”
4.  In “Windows Service Identity” ensure that the identity is either “Local Service” for a single tier machine or “Network Service” for a dual tier machine
5. In “Web Service Identity” ensure that “Report Server” is selected for both “Report Server” and “Report Manager” then click apply
6. In “Database Setup” ensure the host name of the data tier is entered (server name if single tier), “ReportServer” for the database name and “Service Credentials” for the credentials type
7. LEAVE SHAREPOINT INTEGRATION BLANK
8. On the “Encryption Keys” page click the delete button then OK.  The only items encrypted at the data sources and we will rebuild them in a later step
9. In “Initialization” ensure that the host name of the report server is listed as “Initialized”, if this is not the case select the server and click initialize
   

Your server is now back to the default settings for Team Foundation Server, all we need to do now is recreate the Reporting Services data sources for Team Foundation Server.  Please follow the steps in this post to set them up.

After this should be good and cooking.

Jason