If you have a digital camera that uses Smartmedia, do not use the same card for your WK-series keyboard and the camera.   Doing this alone could considerably extend the life of your Smartmedia card.

The heart of the problem is that memory cards keep track of their available space differently than most (current) computers do. For the techies, the detailed explanation is that most memory cards use a 12-bit file-allocation system, vs the 16 bit of DOS and early Windows, and the 32 bits used in Win 98, ME, 2000, or NT. Likewise Macs: They all use 32 bit file systems these days. One consequence of these differences between computers and cameras is that *sometimes* when a computer writes something to a memory card, it'll garble the file structure so a camera can't recognize it any more. Worse, because of the mismatch between how the computer keeps track of files, and what the card is set up to handle, the computer can even mess up a card's file system to the extent that the computer itself can no longer sort it out. Not bad enough? Try this: It's possible for a card to get so messed up that neither the computer nor camera can even *reformat* the card to let you start from scratch! (Apparently, the reformatting process needs to move some data around to get started, and if there's no place to move that data *to*, the reformatting process can't proceed.)

Try not to use a Mac.  Do not use Windows Explorer to move files.

Now, astute readers will note that I said the problems come when the computer *writes* to the card: That means we should be OK if we only read from the card, and don't write to it, right? Well, read-only in the card readers is a good practice, but won't by itself leave you 100% safe, especially in Macs. The problem with Macs is that the memory cards appear as DOS (Windows) volumes to the Mac's OS. In order to keep track of its own Mac-ish things, the Mac OS will write certain housekeeping files to the card, even if you never try to actually copy anything onto it. On the Windows side, the Olympus folks seemed to indicate that things could get written to the card when you wouldn't expect them to, but I don't recall that they gave any instances of how that would happen. (Certainly though, "Moving" files from the card to the computer via Windows Explorer is a no-no, because the computer in that case is erasing the files from the card after they're copied, which means it's messing with the file system again.)

So what's the solution? It turns out to be pretty simple:

1) ONLY read from your cards while they're in the card reader, never write anything back to them.  Writing to the card using Casio's DMS software seems to be safe.  I have used Total Commander and it seems to work fine also.

2) Never erase files from the card in the card reader (including "moving" them in Explorer), or (especially) use the card reader to format the card through the computer.

3) ONLY erase and reformat the cards in your WK keyboard.  (Just another way of saying (2) above, but it's worth repeating.)

4) For camera users ONLY (no need to do this with the WK-series).  Every 3-4 batches of photos, reformat the card in your camera. (Don't worry about this reducing the lifetime of the memory card: Any current-technology memory cards have a life measured in many thousands of write/erase cycles - I guarantee you'll lose the card or it'll be obsolete long before you run out of write/erase cycles.)

Sally from Olympus said she's followed these guidelines religiously, and now owns cards that are a couple of years old, and which have been in and out of various cameras and card readers literally hundreds (thousands?) of times, with 'nary a hint of a problem.

Oh - it's also worth mentioning that CompactFlash cards aren't entirely immune to this problem, even though they're less susceptible to it, thanks to their onboard controller chip. - Less susceptible, but not bulletproof: Avoid problems, and always erase/reformat inside the camera, or the WK keyboard in this case,  not the card reader.