Two other items you might check:

1. If you are printing a graphic on your cheque (logo?), are you using the same resolution on your printer (300/600/1200) DPI as the other workstations.

2. Are you using any "unusual" fonts on the cheque? If so, have these been installed on your workstation?

I am interested in seeing if we can determine what is causing this behaviour before writing it off to "Act of Windows" - oh yes, are all the workstations running the same version of Windows?