iPod iTunes says cannot read write to my hard drive

[Dr Kevorkian94]

well i just downloaded some movies to my desktop and when i drag them to itunes to be put in my library it lodes like less than a quarter of the way and then gives me this: Attempting to copy to the disc "MACINTOSH HD" failed. The disc could not be read from or written to. I don't understand the whole computer works fine itunes and every other function is fine but this is what i get. so as you can see i am in a bind here i checked everything i looked at the permissions on the hd and i am in there for read and write also i have room on my hd so i cant think of anything. before this i was importing a lot of movies it is just i thought it was this one then i tried another and that wont go in either.