Some of you may encounter this anytime. You may be able to transfer files without having any problem in the previous but you're still prone of getting the error "Cannot copy file. Disk is write-protected," or something similar to that. I'm not sure what exactly causes this but I got a solution that may work for you, the same way it worked for me. It's actually simple. Remove your memory card and insert it again. Then try to transfer files again. It's what I did when I encountered this problem. Hope this helps. Good luck!