Thanks to everyone for all the helpful suggestions.

Regards,
Jody

For completeness on this topic, though apparently not your problem here --

Another possible source of a discrepancy between subledger balance and General Ledger control account is the posting of a credit or adjustment where the GL account assigned is the same as the AR control account.

The result is that the Customer account is credited, or adjusted, but the change to the GL Account is zero.