The odds are that you changed your password, and your printer is still trying to use the old one. Your password is kept in the Mac Keychain. If you go to the print queue, it says the job is Waiting for Authorization. If you hit the refresh arrow it will prompt you for your username and password. Enter the new one and check the box to save it to the keychain. This will update the password and save it for future printing. Note that you’ll have to do this every time you change your password, and on every network printer that you use.