Right, the solution has appeared just as suddenly as the problem first appeared. As I needed to print something urgently, I connected by USB. This worked fine. I then disconnected the USB cable to see if the problem was still there. And it printed immediately. So I don't know why it suddenly stopped printing and I don't know why it started printing again, but hopefully this post may help someone with the same problem in future.
Yesterday my Phaser 7500DN suddenly stopped printing over the network. I can send a PDF file to the printer but when it arrives it just disappears.
DNS is enabled but the Confirmed DNS Name is None. The Requested DNS Name is XRX0000AAD5CE99.lan. Name Server IPv4 Address is 192.168.1.1. IPv6 is disabled.
I have read that the problem can be fixed by installing the latest firmware version, but that was for a different printer, so I'm not sure if it applies to me. The firmware is the original factory installed one.