Encryption Credentials Have Expired
This is a bizarre error message that popped up on a mac when I was trying to print. Googleing the error produced equally bizarre results. With one of the solutions from HP being you would have go into the printer via it's ip address and add a certificate. This seemed rather odd for a printer. However upon further inspection it looks like when I added the printer into the mac the default driver came up as secure airprint. Why Apple? Why? This obsession with security has gone too far. The solution was to delete the printer using the minus sign and re-add the printer using airprint and not secure airprint. This resolved the issue for me.