This response did not answer her question. And I have the same problem.
I inherited an accounts receivable ledger "customer" that was set up through a series of journal entries. The balance is net zero but shows as a hundred lines in my open a/r report.
I have cleared all the debits against matching credits (this only worked if an exact match). When I try to clear the remaining debits and credits (again they net to zero), I get "must enter a transaction amount". I did not get this error message when clearing the exact matches (even though my transaction amount was also zero).
Screen shot of the error message:
