From time to time, depending on your printer and printer driver, it's possible for the print queue in OS X to get really hung up. No more items will print. Here's one quick way to clear that print queue.
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For awhile, I was having a problem with my HP printer. (I'm using OS X 10.11.3.) It would print one document, and then the print queue would hang. Pressing the (x) cancel button at the end of the progress bar did not work. The problem cleared up when I updated my HP print driver.
How did I know the print queue was clogged? Apple > System Preferences > Printers & Scanners > Open Print Queue...
Arrows point to symptoms of frozen print queue. Progress bar doesn't clear and "In Use" stays lit.
Doing a little research, I found that there's a nifty UNIX command that will clear the print queue immediately. Open the Terminal app and type:
cancel -a
That command instantly clears/cancels all print jobs. You can find out more about this command from the command line by typing:
man cancel
Note: "man" is short for "show the manual" for that command.
This is a perfect command to turn into a double-clickable desktop file, as described in: "OS X: How to Convert a Terminal Command Into a Double-Clickable Desktop File."
This printer problem was short lived for me, so I haven't researched other methods. If you've discovered another way to force the print queue to clear, let me know.