I have a Sandisk 256 MB SD card and have had problems with it since day one. When I copy large files over, it would seem like everything is copying over fine, then I would get a "not enough space to copy files" error message. But I would be nowhere near the 256 MB limit!! Then I would notice there were a bunch of empty folders in the card. Like about 20-30 of them. When I would try to browse the card using my Axim it would say the card needs to be formatted, so basically I lost all the data that I had on the card. I would get the same problem when I tried to make backups onto the card. For some reason when you copy a lot of data to the card at one time, the card would corrupt itself.
So I bought a 6 in 1 Reader/Writer from Buy.com and haven't had any problems since. It seems 10x faster than using the Axim to write to the card. It supports USB 2 but I don't even need that cause I'm satisified with current USB speed. I recommend it to everyone who is having a Sandisk SD card issue. They used to sell it for $20 after rebate but it's $27 now. Still a good price to get rid of that headache!!
Here's the link:
Sandisk 6 in 1 Reader