Whatever the reason for not being able to print, here's a little secret you may not know. Many times you can have the coupon mailed to you!
Now this won't usually work for sites that offer multiple coupons to choose from (like smartsource or coupons.com )but will work for many single coupons offered on places like facebook and manufacturer's websites.
Just look at the bottom of the print page for the help link like in the picture below. You can click the link and have the coupon sent to you!
Once you click on the help link you should see a box like this one. If you don't see it, make sure the “Resource” tab has been clicked.
I know this doesn't help much when you need the coupon right away but at least you'll have it for the next time and you don't have to worry about your store not taking if they don't accept printables! Hopefully, since it's a mailer it will have a longer expiration date than the one from your computer 😉