Like anything else... try downloading the original iso and making your own psp version... leaving the compression setting to the lowest (larger file size). This always fixes freezes with me.
Done this with PAL, NTSC-U and NTSC-J versions of the game, still to no such avail.
This happened to me but with Chrono Cross, all I did was change the ID of the game to one that works and got passed the freezing point, but with that the quality of the game went down a bit, nothing big though and I barely noticed it after awhile, it was the music that stuffed up sometimes. Also try using pops loader, y'know playing it on different firmwares, that worked for Destruction Derby 2 which only seems to work on 3.11 firmware.
I've changed the GameID to SLUS 01222, SLPS 01222 and SLPS 01490 all of which don't work.
Since I'm a real newbie from only having my PSP for a week, I read up that I might need to downgrade back to 3.40, is there any easy way of doing this?