Mac cannot print to one printer but can print to it's identical twin.

So I have a client with a couple of Apple MAc's for the design team. They have two identical HP CP5520 Colour LaserJets, even built in the same month, same firmware, etc. One of the Mac's can print to one of them and not the other. Just hangs at "Printing - Connected to Printer" until eventually it pauses the printer. I have tried both via "Secure AirPrint" and the other driver listed which I assume is Jet Direct. Both methods work fine with the other printer.

I have compared every web manage page and cannot see any differences other than, and this sounds completely irrelevant, in the General Troubleshooting page, one of the pages auto-hides the options for the paper path test, and the other doesn't.

Very confused. Off to find out how to turn the CUPS web interface on to see if that tells me anything.
Marco van BeekManaging DirectorAsked:
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bbaoIT ConsultantCommented:
it sounds like the problem printer is not connected to the Mac, or the Mac doesn’t reach that printer at all. please first check the printer’s host name and IP address in the Mac settings agianst that problem printer, at System Preferences > Print & Scan.
Marco van BeekManaging DirectorAuthor Commented:
The printer works fine if I set it to use the generic PCL driver (albeit in black and white), and the identical twin printer works fine with both driver options.
JohnBusiness Consultant (Owner)Commented:
On the problem MAC, can you remove the printer entirely, restart and install the printer again?  That very often works in a Windows environment of "same" printers.
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Owen RubinConsultantCommented:
John beat me to it, but I fully agree with him. Delete that printer and add it back. It also works in Mac environments too.
bbaoIT ConsultantCommented:
please double check the protocol used to operate the printer, as shown HERE. make sure it matches the printer model or the same settings on the other working printer.
Marco van BeekManaging DirectorAuthor Commented:
Okay. Never worked out what the deal was, but there was a new firmware for the printer model, and that fixed the problem. I have read somewhere that it might be to do with certificate strength and a recent Apple update, but why it was only affecting one printer and not the other when not only were they bought at the same time, but the serial numbers were only a couple of digits out and were build in the same week.
Marco van BeekManaging DirectorAuthor Commented:
If anyone else comes across this, check the printer firmware.

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