Cannot copy the file exists

I am simply trying to copy a dll file into the Windows\system32 folder in XP Pro SP3.  It keeps saying "Cannot copy <> the file exists"  I've unhidden system files, cannot see it in that folder.  I tried deleting it via command line, says the file cannot be found. I've tried connecting to the system32 folder over the network to copy and it did the same thing...It's also doing this with a few other dll's that I need to copy to the same folder.  I've rebooted, scanned for viruses, updated windows....any ideas?