I'm using TFS Preview (Team Foundation Service) with one of my projects with Visual Studio 2012. I'm also using an on-premises TFS server with most of my projects. When I use my on-premises TFS after using TFS preview and go back to using TFS preview, I get this error:
TF30063: You are not authorized to access MyProject\DefaultCollection.
If I go to Team → Disconnect TFS and then connect to TFS preview again, I'm able to see a "Loading identifiers" loading screen coming up, but in the end I don't get to enter my credentials to TFS preview (my Microsoft account) and as a result, the TF30063 error still occurs.
I suspect this has something to do with my Microsoft account (i.e. Live ID). I'm logged in to Windows with the same Microsoft account that I use at TFS preview. I have logged in to other sites (Windows Development Center, MSDN, etc.) with other Microsoft accounts, but I verified that if I log out of these services and re-login with the correct Microsoft account, I still get the TF30063 error when I try to log in to TFS preview from Visual Studio.
I solved this issue by using the browser from within Visual Studio, View->Other Windows->Web Browser; Ctrl+Alt+R (or * Ctrl+W, W* in VS versions before VS2010) to navigate to the TFS page and log out of the wrong account and log back in.
For me, the issue was caused by using another live-id to unlock a windows phone for development. Somehow the credentials got cached, it seems.