Could not get dependencies for project reference

I have a C# solution with a website project and a C# library. When compiling the solution, the website gives the message:

Could not get dependencies for project reference 'MyLibrary'.

This does not stop the wbsite compiling and running until I try and build it with a TFS build, when this error message fails the build.

What does this mean and how can I get round it?

How do I get project Dependencies in Visual Studio?

On the Project menu, choose Project Dependencies. The Project Dependencies dialog box opens. On the Dependencies tab, select a project from the Project drop-down menu. In the Depends on field, select the check box of any other project that must build before this project does.

How do I add a reference to a shared project?

You add references to a shared project just as you would a normal project reference. In Visual Studio or Fire, you right-click the "References" node of the real project and choose "Add Reference", and then pick the shared project from the list.

After trying many things, I realized something. The error was never going away, no matter what I did to clear the builds and such. I closed and reopened the solution and it went away.