As much as I love my MacBook and iMac, I will admit I have more problems printing coupons then others. I have noticed a big difference since the latest update of os Lion. Thanks to Mich-ael on Facebook for finding a solution. I hope that this helps you also if you are having problems not only on a Mac but on a PC as well.
This is what Mich-ael found:
We’re sorry to hear about your trouble printing. An update has been released to support printing on Safari 5.1 browser in native 64bit mode on Mac OS X Lion. You should also be able to print from your Firefox browser. If you have previously installed the Coupon Printer and cannot print coupons, please uninstall the Coupon Printer and reinstall it from this link http://print.coupons.com/c?ouponweb/help/print/instal?l.html to get the latest version. We hope this information has been helpful, please let us know if you continue to have issues printing by sending an email to firstname.lastname@example.org. Thanks for your support and cooperation
When you go to that link there is also the coupon printer update for Windows!
Hopefully that will help, I also have a few older posts that you can look through if you need more info and help.
Let me know if that worked for you!