Hey!
I just switched to Unity 4 with the newest Playmaker. What I discovered right away, is that almost every setup that is bigger than 3 (or so) object with 3 state machines gives strange errors. It also pauses the editor. You can't turn off the error pause. It pauses anyway, whether it's on or off.
Most common errors are the ones in attached jpg. (I checked, those make no sense: "Compute mesh inertia tensor failed (...) supply a tensor manually". On every object in the scene, rigid body or not.)
I thought my Playmaker character setup from Unity 3.5 was wrong somehow, so I started doing the character from scratch in Unity 4. Everything was working fine with no errors in editor, until I got to the point when I used SmoothLookAt Action on the head of the character. ERRORS, endless errors and game pauses right away. I deleted the SmoothLookAt, because it worked fine before. Still nonsense errors.
Btw. the game runs fine and smooth if you make a Build. It's just the editor.