Try this:
With the KM editor running, choose the menu item View > Select Last Aborted Action and the editor will take you to the action that experienced a problem.
Note - if you have several macros that are failing you should try this after the macro you are most interested in fails, otherwise you may be pointed to a failed action in some other macro.
I don't know how effective this will be with your giant macro 
but it might be informative to you.
You might also find this thread useful:
which includes a method for searching for an action by its ID.