Error initializing task PackageFilter: Not registered task PackageFilter. What does this mean?

So, whenever I try to build my solution I get the error: "Error: Error initializing task PackageFilter: Not registered task PackageFilter. (Name og project in solution)".
I have no clue how to solve this, the solution contains about 20 diffrent projects, the one specified in the message is a console app, the others are libraries, forms and websites. Please help. The solution works perfectly in visual studio on windows.