Watch out for foreign characters in file names
Hi all...
Having come across this problem a few times myself, I thought I'd post this reply just in case none of the above solutions don't work for you. Although the above are all valid, there is ANOTHER reason other than these that you may receive this error even if your drive is operating perfectly: Foreign characters in file names, i.e. extended character sets.
If you're trying to copy a file to an external drive / memory stick that is formatted as NTFS for example, the file system may not support these; and YES you CAN copy only NTFS drives if you're running the appropriate third party software on your Mac to do so (I'm using Paragon NTFS for Mac OS X).
Example of a problematic filename: Felix Kröcher - Scheint.m4a <-- Notice the double dotted 'o' in 'Kröcher' (assuming this editor supports display of the character set).
Hope this helps out someone in the future as it had me a little perplexed for a while.
Regards, Adrian.