OKI C511DN won't print

Hi. I've been using a C511DN for some years with few problems. a reliable workhorse.
However this week I tried to print a DTP document and I got an error message. I hit print again, and it printed, but printed one page from the document twice. I then printed it again, and I got the error message and it hasn't printed since. I've followed the instructions from tech support but still no printing. Here are the details of my problem:

To summarise:
1. I have tried printing from two computers and neither works. This suggests it's the printer.
2. I have used the driver removal utility. I have installed a new driver both manually and the normal way.
5. I have taken out the cables and pressed the power button for 10 seconds then left it for 15 minutes. I have done this twice. (This is supposed to clear the memory).
6. I have tried a different USB cable.
7. When I try to print I get an error message - a popup on Windows, and also in the Print Queue. But no error message on the printer.
8. It can print a test page using the actual printer menu buttons. It will not print a test page using the PC.
Any thoughts of something else I should try?
Thanks