Don't think it's a coincidence in my case. Here's what I did:
Installed the newest UltimaROM, gave me the network error.
Restored my previous ROM, it was the Nightmare. Network worked fine.
Just to make sure, I did the above steps again, thus recreated the network error and went back to my old ROM successfuly.
After that I flashed Ultima again (the same newest), this time with normal XEMC3, network worked, 3g worked, but Phone process stopped every time I tried to access mobile network settings.
Restored again the Nightmare ROM, tried to access mobile network settings, worked without a problem. Still running it. 3g/cell signal is fine.
Using CWM 188.8.131.52 at the moment.
Else I'm missing something completely.