I was stumped by this. New ProGraf 4600 suddenly stopped printing from Lightroom. I was sending a large print 44 x 52 to a roll 44" wide as a proof. It would go through the motions of printing -- the file would show up in the printer queue, and then I'd get a "the printer is not responding" error. The printer never started the job. Tried the job from Photoshop as well -- same result. I had previously run prints from Lightroom successfully -- this was a new development.
I ran a status print from the LCD. That printed fine, all across the roll, which is a nice feature, since it wastes less paper. Ok, the printer hardware is working.
From the Printers/Faxes panel, the computer sees the printer and is able to retrieve Ink Supply status. Using the Printer Utility, I tried updating the Media Settings, and got a 306A Communication Error.
I rebooted the router. The printer retained the same IP4 address. I rebooted the printer, and tried printing again. Same "printer not responding" error in the print queue.
What finally fixed it for me was removing the printer and reinstalling it. I am using an IP address, not Bonjour. It doesn't immediately show up in the choices, so I added it manually using the IP and Subnet mask addresses it had before.
This time when I went to update the media settings, it saw the printer, and did some housekeeping. Opening up Lightroom again and sending the print the printer was successful.
TL;DR -- Reinstall the driver, check the IP settings, reboot the router and the printing application for a 306A error.
Posting this because I could not find anything comparable doing a search of the interwebz. Hope someone finds it helpful.
