Every time I open my VS solution I get “Projects have recently been added to this solution. Do you want to get them from source control?”

Thanks to some research and trying some various options this is what solved it in our case.

1. Unbinding the solution file from TFS

Unbind the solution file (.sln) from TFS. We did this (in visual studio of course) by going to the menu File => Source Control => Change Source Control.

2. Cleaning the solution file by deleting globalsection

We had to clean the solution file (.sln) by opening it in a text editor (we used notepad++). We removed all occurences of GlobalSection(TeamFoundationVersionControl) = preSolution. Including the mentioned starting tag and the ending tag EndGlobalSection.

3. Bind the solution file to TFS again

Finally we binded the solution file (.sln) to TFS again. We did this (in visual studio of course) by going to the menu File => Source Control => Change Source Control

Thanks to http://www.nivisec.com/2008/09/vsts-projects-have-recently-been-added.html who pointed us in the right direction after some hours of research.