Sounds like you are talking about two differnt versions of the firmware. Did they ever actually release a 3650 phone with MIDP 2.0? I know they were planning on it. If its not that its just some weird bug difference between the firmwares, see if you can isolate the bug alittle better.
Figure out where the bug is coming from, illegal state exceptions allways come from API calls, the first things I would look at are:
-sound API usage
-recordstore calls (perhaps you are trying to access a recordStore that has already been closed)
-calling a dead graphics object
Things like that.