Today a client contacted me and said he gets an error while working with Excel. I found that the error massage TF84012 does not have interesting documentation or history on the web. After talking to the client again I tried to imitate the steps he did.
Then I found the real problem. The first time he connected to the TFS 2008 everything was OK. but after adding a new column he actually got another error: TF84034. that was the real problem. Solving the problem now was easy, I just followed the simple instructions in granth’s blog about installing the KB946458.
So keep in mind, even if you get the TF84012 error, the solution could be the solution of the TF84034 error.