"The drive cannot find the sector requested."

[conquest!]

i have downloaded a video from Youtube onto my computer.
it is now in mp4 format. this works fine and plays perfectly in Windows Media Player.
however, when i try to send it to my phone, which is connected by USB, it says "The drive cannot find the sector requested." and does not send the video to my phone.
what does this mean?
do i need to change the format?
thanks (:

[ChuckFickens]

if it's a memory card in the phone sounds like it may have got corrupted. copy what you can off it it so you don't lose it and try reformatting the card, the phone should have an option to do this somewhere.