First, let me state this was a self-induced error. I'm still loving this printer but thought I'd share this experience.
I was ready to crank out a print from Qimage. I did all the normal activities and Qimage obliged nicely.
Then I realized I'd used the wrong profile. The print job had already been spooled to Windows but hadn't started printing so I went to "Printers and Faxes" and canceled the job. Unfortunately it would appear that some of the print job made its way to the Z3100. What eventually resulted was the 79:04 message and the need to reboot the printer.
Everything is fine with the printer. It continues to produce stunning prints.
I've looked and looked and couldn't find any way to stop a print job in the HP Color Center. Did I miss something?