This could be a fault with the card or with the contacts on your card reader.
When you purchase a Smart Media card it should come with a small, circular, metallic sticker. Most people just throw these away but they are there for a reason. To write protect the card you have to apply the sticker to the 'wrtie protect pad'. (To see where this is, look at the 'plane view diagram here:
http://www.pcmcia.org/smartmedia.htm ). Now, somehow or other, your PC thinks that there's a (non-existent) sticker on your card. You should check that there's no dirt or anything on your card which could be causing this error. If you've got another card, try this in your card reader - if it works fine then the problem is definitely with the suspect card rather than with the card reader. If your card reader is OK and cleaning the dodgy card's terminals doesn't help, then, unfortunately, it might be time to consign the card to electronic heaven.
Chris