Hm I just updated: Unity 6000.3.0f1 with Playmaker 1.9.9p1:
"GUI Error: Invalid GUILayout state in FsmEditorWindow view."
and
"TypeLoadException: Could not resolve type with token 01000186 from typeref (expected class 'UnityEngine.EventModifiers' in assembly 'UnityEngine.IMGUIModule, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null')
HutongGames.PlayMakerEditor.FsmGraphView.HandleMouseDown () (at C:/Projects/Playmaker_1.9.1/Projects/Playmaker.source.unity/Assets/PlayMaker/Editor/Classes/FsmGraphView.cs:1275)"
I can't link states in Playmaker Editor, I can't drag states, basically I can' work with the mouse in Playmaker Editor. I guess this is because of those errors?