We had a customer who suddenly cold not print checks after using PayWindow for several years. The printer was giving her a wrong size paper error message. It took us about a week to finally find that they accidentally checked the Dot-Matrix Code option in the check printing settings.

That is only for users using a dot-matrix pin feed printer with special pin feed checks that are only about 5.5 inches in page length.

That option is item number 4 on this page in the help file:

http://zpay.com/pw-online-help/PrintingChecks.htm