I've been struggling through a Team Foundation Server 2008 install with Sql Server 2008 over the weekend. It seems to be having an especially hard time with the SQL Server Reporting Services. After analyzing a few things, I determined that the configuration tool was having an issue due to some prior installations of software. The report urls were pointing to a SQL Express directory.

I went about setting up the virtual directories manually. This required setting up an application pool, and I assigned my service user to run the pool. After I did that, I had to grant the user write access to the RSTempFiles folder. Then I received an error when browsing the site, "the path is not a legal form."

I couldn't find a site anywhere with a solution, though there was a dead thread on the old msdn forums with the same problem with SRSS. Since the tubes held no hope for me, I had to resort to old fashioned troubleshotting.

If you receive this error, you need to add your application pool user to the SQLServerReportServerUser (followed by $servername$instancename) group. It's that simple, but the error doesn't indicate what is necessary to fix it.