Call AddBugAction1 action from Test lab module custom button

Hi

I've added a custom button in Test Lab module to launch the New defect detail page. Here is what I have in workflow script and it doesn't launch the new defect window when clicked on button. It does show the msgbox windows. Please help what's wrong in it.

Function TestLab_ActionCanExecute(ActionName)
   TestLab_ActionCanExecute = DefaultRes
         Msgbox ActionName
   If ActionName = "UserDefinedActions.TestLabDefect" then
            Actions.Action("BugAddAction1").Execute
   end if
  TestLab_ActionCanExecute = DefaultRes

End Function