Whoops, we have just finished testing all possibilities and we have figured out that your plugin is having a conflict with the MyPuzzle Word Search plugin. However, Print-O-Matic, without MyPuzzle Word Search plugin, doesn't fail on other pages. We have tried Print-O-Matic 1.4, 1.5a, 1.5.1, and Print-Pro-Matic with all the recent versions of MyPuzzle Word Search. We have found that in version 1.4 and 1.5a of Print-O-Matic there is no conflict with MyPuzzle Word Search. In versions 1.5.1 and Print-Pro-Matic the conflict causes Chrome's print interface to not appear on top of the pop-up, as well as other browsers. Now you must right-click and click Print or type CTRL-P on Windows to access the interface.
In versions 1.5.1 and Print-Pro-Matic the conflict causes the Print Page CSS to not appear in the print pop-up.
In versions 1.5.1 and Print-Pro-Matic we validated that the "do_not_print" works in preventing the display of such data in the print pop-up, but when closing the pop-up and returning to the HTML page the said "do_not_print" items remain unseen. This appears to be because the unseen element isn't being called again after the pop-up closes.
Since your past plugin software had no conflict with MyPuzzle Word Search in any manner, my guess is that a change has occurred in your code that is causing a conflict. Although, I don't know what this may be.
Thank you so much for all of your assistance.