Alright... I am about insane(not that is that far to go )
I SWEAR I can not see the problem here. The following gives me a expected expression error on the first line.
Code:

If (UserInLocalGroup($ComputerName, "Users" , "Domain Users") = True)
  ? "Domain Users present on " + $Computer
EndIf

Function UserInLocalGroup($ComputerName, $Group, $User)
  $GroupObj = GetObject("WinNT://" + $ComputerName + "/" + $Group)
  
  $FlagFound = False;
  For Each $UserObjG IN $GroupObj.Members  
    If $UserObjG.Name = $User
      $FlagFound = True
    EndIf
  Next
  $UserInGroup = $FlagFound
EndFunction