“Exception has been thrown by the target of an invocation.” when building a Visual Studio 2010 VSPackage

I recently create a couple of VSPackages for some Visual Studio extensions (menu bar/command). I compiled them correctly yesterday, checked into TFS (i'm the only one touching this project, FYI). I had already installed these extensions and were working fine. Today it doesn't compile! I get the following error:

Exception has been thrown by the target of an invocation.

This doesn't tell me anything, so i fired up Visual Studio with the following command:

devenv.exe /Rebuild > out.log

In my out.log, I see the following:

C:\Program Files\MSBuild\Microsoft\VisualStudio\v10.0\VSSDK\Microsoft.VsSDK.targets(420,5): error : Exception has been thrown by the target of an invocation.

I have been stuck on this for hours and can no longer build these VSPackages. Anyone? This is really frustrating. I have already tried cleaning project/rebuilding/build using Visual Studio itself (not command line)