Add mpf 11 project to a Portable Class Library as reference

Hello,

I need to be able to add my custom mpf project for VS2012 to the references of a Portable Class Library.

If add the reference using the browse window, no problem it is working: it adds the dll.

But if I choose to add the reference from the solution projects, the mpf project is rejected and throws "unable to add the reference".

The TargetFrameworkVersion and Profile are matched, so I think the problem comes from ProjectTypeGuids or a property page not able to display the Portable Class Library extension. But I don't know how to moke/fake a Portable Class Library project in mpf 11.

Thanks in advance for your help.