Can't copy files from Firewire device

All of a sudden I can't copy files from my firewire device to my hard drive or to a networked computer or server. I can open the files and "save as to any device, but I can't copy from the finder by dragging. I can copy to the firewire device by dragging in the finder. I have had this problem once or twice before, but it went away after a restart and this time it didn't.