Hmmm please post more info on that, it sounds way to easy.
what was the phone model you changed the imei in, and have you checked imei with other prog so that its really the "new" original imei.
I have changed imei in a 8210 and i got a chksum error but i fixed that, but the probblem is that the phone checks the chksums with mad2 memmory
so phone keeps restarting because internal prog dosnt boot properly then.
Regards Leeloo