(destination is a SD-card)
However, you may want to monitor your resources during the copy (ctrl+shift+esc) to see if windows itself is what is freezing instead of foobar. Are you able to interact with programs other than foobar during the "freeze"?
Have you tried copying from a command line instead of explorer?
You may also want to clear up some free space and defragment your hard-drive to speed up the copying process.
Is the SD set to read-only?
Are you playing songs in foobar from the SD card that you are copying to?