Hello, I don't find a lot of cures for that, but might see the last post here...Re: iTunes Error - attempting to copy to the disk "Macintosh HD" failed
When itunes 9 was released, they also offered a different way to organise media.
Instead of putting music in "iTunes Music" it gave the option of putting things in "iTunes Media/Music".
Try putting things in the itunes 9 organization. Do this by going to the file menu.
Select Library > Orginize Library. If you can select "upgrade to itunes media arganization". Then click OK and let it reorganize your library. If you cannot select this (becuase it is grayed out) then itunes thinks it is already using that method. In this case, try renaming your "iTunes Music" folder to "iTunes Media" - apparently in some cases itunes did not make this change, which might be what is confusing your ipod sync. Be prepared to rename this folder back to what it was in case it causes problems . . .
Resetting the iTunes Media folder location resolved this issue for me.
I started to get this error message when backing up my iPhone:
Attempting to copy to the disk "" failed. The required disk cannot be found. OK
Based on solutions that other parts of this thread link to, I decided to check the iTunes Media folder location preference setting (iTunes > Preferences > Advanced > iTunes Media folder location). I'm not sure how it happened, but the location text field was blank when it should have shown the file path to my iTunes Media folder.
After resetting the location (to the same "iTunes Media" folder that I've always been using), I was able to sync my iPhone as expected.
So, it seems the error message pertains to iTunes accessing your iTunes Media folder. The trick is finding out what is causing it to not do so.
If you're having this issue or something close to it, start with iTunes > Preferences > Advanced > iTunes Media folder location; then, continue from there, verifying that iTunes has a location that it can read and write to.