TF400324: Team Foundation services are not available from server in Visual Studio 2012

Question

When I open my existing solution in Visual Studio 2012 professional, I got the above error. This used to work but something messed up after the computer is rebuilt.

Answer 1

...better late than never...
I just had a user run into same error TF400324 connecting VS2012 to TFS2015 (hosted in a virtual private cloud). TFS Web Access worked fine for her, but Visual Studio 2012 UI was stuck in offline connection.

FIX: She managed to get VS connected again after clicking Team Explorer > Connect | {TeamProject}, Then select desired Team Project below the TFS Server connection (see screenshot attached).

NOTES:
I suspect clearing client-side TFS cache might also fix, but all VS instances would need to be closed then "Connect to Team Project Connection" re-established. Just disconnecting and reconnecting VS to TFS did not clear the "offline" state.

Error she saw was in VS output window:

This solution is offline. [Team Foundation Server: {//TFS Collection URL}] The solution was offline during its previous session and will remain offline. TF400324: Team Foundation services are not available from server . Technical information (for administrator): Page not found.

NOTE: I recently moved TFS to different domain requiring SSH connection and localhost port mapping. I have users going offline much more frequently due to different proxy routing depending on whether they are at work or connected more directly to the Internet.