Warning displayed when adding solution to Team Foundation Server 2010

Your solution folder structure should resemble:

Solution Root folder
├── .sln solution file       
│
├── Project1 folder
│   └── Project1.csproj   (or .vbproj)
│
├── Project2 folder
│   └── Project2.csproj   (or .vbproj)
.
.
.

For me it was like this that I tried to add the solution from another location already. I then had to clean the workspace which was created for the other location.

For Visual Studio 2013 you can find the workspace settings under:

File -> Source Control -> Advanced -> Workspaces...

1. On the Manage Workspaces dialog select your workspace you work with
2. Hit Edit....
3. On the Edit Workspace <yourworkspacename> dialog
4. clear the "wrong" location

Try to add the solution again.

As described in this Visual Studio forum post (link below), the basic issue is that a project in the solution is outside of the sub-tree that the solution itself is in. This can possibly lead to problems if another user maps the different subtrees differently in his workspaces than the user that is checking in. The cross-tree references will no longer work. The dialog is only a warning, but can be continued if you know your team doesn't split up the code tree with complex workspace mappings.

https://social.msdn.microsoft.com/Forums/vstudio/en-US/29579a28-9de0-4fc6-a253-b38191aa4fdc/must-projects-be-added-under-binding-root-of-solution?forum=tfsversioncontrol