C3760n printing errors

I have two C3760n printers that have worked for years.  Suddenly both of them are coming up with various errors such as Access error, authentication failed, user invalid (016-536 and various other 016-xxx error codes that are not listed in Dell's troubleshooting documentation).  These printers can be hooked up to USB or ethernet and the problem remains the same.  They will not print, thy just come up with these errors.  I have updated the firmware on the printers, reset them to defaults, updated drivers... what is going on here?