This means that there was an error when copying the file to the new location.
The files at the source location are untouched.
It usualy append when you try to write a file to a disk location that is already used by another file, but is not yet marked as in use.
You only need to restart the copy operation. You may need to suppress a file or two in the destination location: The last ones that have been copyed.
Electro, April 2011