I have had this issue several times. If you have access to a windows machine, just plug your N900 in via USB, and run the disc checker utility. Once it's finished it'll clear the corrupted data and everything should run fine again. Are you running your N900 overclocked? I usually run my OC with XLV at 250-1150 during normal use because it goes unstable with ULV. If I try to run transmission at these settings it will reboot, so I have to drop the clock speed to 250-1000 to keep it stable. Hope this helps.