Have you checked data integrity?

Data may need to be re-indexed.

Is there an item on the invoice that, if repeated, would result in the additional $40.92?

The credit in the AR clearing account in GL indicates that $1569.57 was actually posted from OE while $1610.49 was posted from AR. I am guessing that because of an indexing error, the $40.92 was repeated in the invoice calculation.