I might try reinstalling the firmware. It might not do anything to solve your problems, especially if there really is a card problem, but it’s worth a try. Use the Manuall Firmware Update method, described HERE, don’t use the updater unless you know for sure your firmware is outdated (otherwise, the updater won’t do anything).
Also, I’ve been experimenting with Linux recently. It occurs to me that this read-only issue your facing is some kind of Linux feature desinged to prevent an already-bad filesystem from getting (even more) corrupt. The Clip Zip probably doesn’t have any such feature.
I would use fsck to see if I can check the card for file sysem errors. If that fails, try using a Windows machine to perfom a check disk. Or, you can kill the problem by wiping the filesystem completely using the Format option inside the player’s Settings screen. In general, that’s the best way to format anything that’s going to be used with a Sansa product.
