All of my PlayMaker projects appeared to be broken after updating Unity to 2018.1.0f2 (release version). I also tried making a blank Unity project, imported PlayMaker from the asset store, and still received errors.
Using the suggestion to delete Assets\Playmaker\Actions\ProceduralMaterial seemed to make the errors go away for one of my projects, and got things back to a somewhat workable state. I had to pull PlayMakerGlobals.asset from my source code repository and put in it Assets\PlayMaker\Resources to get the globals working again. A couple of the parameters in the PlayMaker GUI had to be redone, but it wasn't too big of a problem.
On other project, I just had to delete the ProceduralMaterial folder and it was working again.