n8 cant delete video file problem. help!!!

[mihgan]

i just converted some videos files and trfd to my mobile n8 ...now when i m trying to delete one of these files it is not allowing me to ...saying its already open...rest of the files can be deleted but theres only a problem with this one file...have tried almost everything reboot my phone ...
tried via computer connecting the usb cable...it either says the file is in use or u do not have the permission to delete this file..really am out of sorts what can i do.
what i dont wanna do is format my mass memory i have installed so many things pls help!!!!!!!!