Operation Could not be completed.
A very common error in the Mac OS X printing system. It is most commonly resolved by pausing the printer, and then resuming the printer and document you are trying to print.
Inconvenient? Yes. However, it’s still much better than having to reboot Windows, the typical fix for PCs with printer issues.
This most likely cause of this error is a compatibility issue with your printer driver, so if you get this error repeatedly, make sure you have the most recent version of your printer’s drivers installed on your machine.