iTunes Error - attempting to copy to the disk "Macintosh HD" failed

have you tried this:

check if you have read & write permissions for your music folder. in finder, right-click on it and +get info+. unlock the little padlock (you may have to enter your admin password) and change the permission settings. next, click on the little gear-shaped icon and +apply to enclosed items+ like so



the important part is to *apply to enclosed items* !

J GG

Do you keep all your music organized by itunes, and all in the same place?

If you goto the advanced preference pane in itunes, what does it list as the "iTunes Media folder location"? do you have keep organized, and copy files ticked?

Inside the folder listed as iTunes media folder, there should be a folder call "Music". This is where iTunes wants to write music - perhaps it does not exist on your system?

I think I'd goto "file" "organise" select both options (if available) and click OK.
This will let itunes organise things the way it wants it.

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".

see http://support.apple.com/kb/HT3847

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 . . .