Android.phone has stopped. Sim card problem.

[Nikouy]

I have an unlocked Motorola Atrix 4g, and today I have changed the sim from one from another carrier, and it show: process.android.phone has stopped.
I have read that it´s because some phones does not work with 64kb sim or 32kb. So I tried with a new sim from that carrier and it continues showing the same message.
The cell phone recognizes the sim card, but the signal instantly gets off.

With my sim card it does not happen...what can I be?
Can I fix it flashing a new rom?

I am with 2.3.6 official rom.

Many Thanks.

 

[ravilov]

If you have an unlocked BL, try flashing a different radio.

 

[Nikouy]

If you have an unlocked BL, try flashing a different radio.

I have not unlocked BL...
Any different idea? I´m desesperated!

What about flashing again an oficial rom? How? Need I to have an unlocked BL to do it?

Many Thankssss!