I upgraded to 5.3 and the latest patch. I tried 1.8 again.. this time it starts with a single red compiler error shown below. If I remove the .cs file in question and hit play, I get no compiler error but I get the same 999+ errors as mentioned before. Here's a few examples, starting with the initial error. Thanks for your help.
Assets/iTween/PlayMaker/Editor/iTweenMoveToActionEditor.cs(8,41): error CS0246: The type or namespace name `CustomActionEditor' could not be found. Are you missing a using directive or an assembly reference?
JumpkickTrigger: FSM: Action: MissingAction: Could Not Create Action: SetFloatValue (Maybe the script was removed?)
UnityEngine.Debug:LogError(Object)
HutongGames.PlayMaker.ActionReport:LogError(PlayMakerFSM, FsmState, FsmStateAction, Int32, String, String)
HutongGames.PlayMaker.ActionData:LogError(String)
HutongGames.PlayMaker.ActionData:CreateAction(FsmState, Int32)
HutongGames.PlayMaker.ActionData:LoadActions(FsmState)
HutongGames.PlayMaker.FsmState:LoadActions()
HutongGames.PlayMaker.Fsm:InitData()
HutongGames.PlayMaker.Fsm:Init(MonoBehaviour)
PlayMakerFSM:Init()
PlayMakerFSM:Awake()
Could Not Create Action: JumpkickTrigger: FSM: State 1: EnableFSM (Maybe the script was removed?)
UnityEngine.Debug:LogError(Object)
HutongGames.PlayMaker.ActionData:CreateAction(FsmState, Int32)
HutongGames.PlayMaker.ActionData:LoadActions(FsmState)
HutongGames.PlayMaker.FsmState:LoadActions()
HutongGames.PlayMaker.Fsm:InitData()
HutongGames.PlayMaker.Fsm:Init(MonoBehaviour)
PlayMakerFSM:Init()
PlayMakerFSM:Awake()