I am using Knoppix 3.8.1 as a Windows file rescue cd, trying to transfer files to a usb memory key. Linux mounts the memory key and I can see files on the key, but when I try to copy them form the hard drive to the memory key I get "could not write to /mt/usba1/filename". The reverse does not work either, cannot copy from key to hard drive, but can copy from hard drive or memory key to a floppy. Any help would be appreciated.

It's been awhile for me, but try cp /mnt/usba1/filename /home/whereever

You would do this from a shell prompt. If this doesn't work, make sure you have the "rights" to.

I believe you will find you are dealing with the typical permissions problem. As in the usb stick and the hard drive were mounted without write permissions, only read permissions.
You might try the following command (I hope it's written down correctly in my notes)

mount -n -o remount,rw /dev/device /mnt/location

device of course being the usb or hard drive
and location the directory you wish to mount it in for access.

Hope this helps,
linuxusr47