Leave it blank?

Or maybe that magical -1 that Lacerte loves so much.

Thanks for the response.  The field is mandatory and can't be left blank.  It will accept a negative 1 and the Form 1116 calculates correctly.  However, a critical diagnostic error appears that says you can't have a negative number.

I wonder why the current year tax withheld amount field is mandatory.

I can assure you it's not mandatory.  If you can describe your case in more details and the exact error you've got, someone may be able to help.