Sony Ericsson :: W890i Invalid Sim Message

I recently bought a w890i locked to the Three network, and unlocked/debranded it using Omnius. I've done this before lots of times, so I know I didn't make a mistake. I have all the right drivers installed and I followed the instructions to the letter.However, when I finished, I noticed that I was getting an "invalid Sim" message. I tried unlocking it again but it didn't help - it said it was already unlocked. I checked the lock status using left,left and sure enough, it is unlocked. So just to rule out a problem with the sim, I tried a few different sims that I had lying around. The Three sim that came with the phone didn't work, and neither did the O2 or Vodafone sims that I tried. but an old Virgin Mobile sim worked perfectly. So what's the problem and how do I fix it. It's possible the problem was already there before I unlocked/debranded the phone but I never checked since I'm not on the Three network.I thought it might be a problem with the CDFS. I backed-up the TA and CDFS from another w890i as a precaution (like I say, this isn't my first time) but I never backed this one up beforehand believing that I could just use the TA and CDFS extracted from the earlier phone. However, now I've read that the CDFS is unique to each phone, so I'm wondering what I should do. What will happen if I try to restore the TA/CDFS from another phone? To be honest, I don't really understand anything about them.I've tried re-flashing the firmware, too. It didn't help. And there's nothing wrong with the firmware - I've used it before. I know I could get the original firmware back by uploading the old CDA and connecting to the SEUS, but would that really help at all?I'm a bit of a novice, in way over my head here.