I recently been working with a client who has been seeing strange problems when they try to create new workitems via a SharePoint portal site on a TFS2010 Beta2 installation. They appeared to have a fully working TFS2010 installation, but when they came in on a morning they found that even though they could login to the TFS created SharePoint team site they could not create a new workitems, they got an “Error 403 Access Forbidden”.
If they logged into SharePoint as a user with system administration rights it all worked fine. Now here is the strange bit, if they then logged in the user who got the 403 error it all worked fine, but when they came in the next morning it all happened again.
Turned out the issue was due to underling file access rights, once these were fixed all was OK. basically only the admin user had enough rights to populate a cache. Why this had occurred was still a bit of a mystery, but it is something you might see on any SharePoint installation. If you see a issue similar to this, the best option is to use Process Monitor to see if there are any file IO problems. This should point you in the right direction