3310 no signal on 1800mhz

[Liam]

I have a 3310

It was originally a 4.18, someone had flashed it wrong so I upgraded to a 4.45 with an MCU+PPM Flash then calculated the FAID, then unlocked it.

All was well until I found it would get a signal on Orange or one2one(GSM1800) for a few seconds then go, BUT, on BT Cellnet and Vodafone, (which are GSM900) it would keep a signal forever.

The IMEI is not blacklisted, it was on BTCellnet from the box. (they dont block IMEIs yet)
I have tried to changed the IMEI and still the same problem

A manual network search will reveal all FOUR networks with a BT/Voda sim, and will not find any with an Orange or one2one SIM.

I have THREE in total which suffer this problem, but the other two dont get a signal at all on any network.

any IDEAS??

[Liam]

It gets signal on Orange (1800mhz) for about 10 seconds then nothing.

even with a different IMEI same problemn

but with Vodafone and BTCellnet (900mhz) its perfect signal

Ideas?