NACHA rules don't extend beyond ACH items. The attempt to use a paper item -- it sounds like it would qualify as a "remotely created check" as that term is defined in Regulation CC -- would be perfectly legal and authorized if the drawer of the original check had agreed to it in the event that the check -- in paper or ACH format -- can't be collected.
That said, the only person to whom your bank could be accountable for bouncing that paper item is your depositor, who has already been clobbered with three overdraft fees by my count, and would probably not be at all bothered by your refusal to pay it.
Just understand, of course, that your customer still owes the money to the payee.
_________________________
John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8