VS2012 $(exists) only accepts scalar values

Question

Okay, this is more of a build error than a programming error. I have never had much reason to get my hands dirty with builds, so this error is baffling me.

I have tried

Answer 1

Open your .csproj file and look for any duplicated import tag.

In my case the .csproj had two lines like this:

Remove one of them fixed the problem.