[Resolved]  Nokia N73 — IMEI Number is not valid

i got a gifted Nokia N73 from UAE . it has some problems like poor service , slow speed , poor battery service, others. so i was returned to UAE for repair , but now it is back to me , but it is not taking Indian SIM cards and after inserting any SIM shows "SIM CARD NOT VALID" .
So please tell me what will be solution for that. somebody say's that it's IME number is wrong .
how the IME number will change or correct.
Thank