Hi.
what version of Unity are you using, and what version of PlayMaker?
to be honest, I would very much refrain from switching to .Net 4 for at laest another year and more. There are problems with this and it's not been fully testing properly it feels. Not that I am trying to dismiss the issue, but as a warning, I had to revert many times back from . net 4 because of random issues ( not related to PlayMaker, it's network stuff)
Bye,
Jean