Hi,
Depending on the steps you did for upgrading, it could be the case.
First you need to update to PlayMaker 1.8 while under Unity 4, verify all is working, and then upgrade to Unity 5.
Have you done it this way?
rehooking could require you to select another fsm and back just for PlayMaker editor to refresh. Sometimes error don't go away straight away.
Bye,
Jean