cannot move file: cannot read from the source file or disk

[crucial]

Ok. So i convert the files to mp4 and i click 'move to device' and all i get is a damn error message saying 'cannot move file: cannot read from the source file or disk'

So now i cant get anything on the psp, which is quite wierd as the first time tried moving a video to the psp using psp video 9 (just a few hours ago) it worked. and now its not

btw my firmware version is 2.81

Any help would be apreciated

ps: i read the sticky and tried searching on the forums and all i got was something about changing my device folder but i have already changed it and stuff.