The Trial Balance should match the GL and NOT the Aging because the Aging takes into consideration future dated transactions.  A lot of people make the mistake of trying to get their Trial Balance to match the Aging.  Go into the GL and see if anyone made a GL entry in either account.

I did check to see if there was a GL entry - no luck.  Will compare it through the end of the year and see if there is a difference.

Assuming you ran a DTR "out of the blue" to see if anything was sitting in there unposted.  Meaning, not on the heels of updating a journal.

When AP and AR were off for me, it usually meant I voided a customer refund check in a different month than I cut it...for what it's worth.

Almost forgot, this happens sometimes when someone post invoices but does not post the Daily Transaction Register. Go to the GL, Main, Daily Transaction Register and print and see what happens. Note that you cannot do it from the AR and AP modules, has to be done from the GL

That was the first thing I though of also.  I will have my AP look for a voided check- that is a good idea.  I will have to keep thinking about AR.