Formatting the card in a card reader probably won't help. Or at least it didn't help me. Or anyone else I've spoken to about it. As far as I know, to stop it asking you for a password, you need to use a nokia 9210, and do a forced erase on the card.
Someone on here said:
"This problem can be solved by this way :
1. You need a Nokia 9210.
2. You need an unlocked MMC (can be borrowed from your friend)
3. Put the unlocked MMC into the memory slot of Nokia 9210.
4. Choose the command that will format the MMC (unlocked MMC)
5. When the fone ask you to confirm the format order, quickly remove the unlock MMC and put in the locked MMC which you want to unlock.
6. Press Ok.
If you're lucky, the locked MMC will be formatted and the password will be also break. Good luck !"
Haven't tried it myself yet, but I'm planning on it as soon as I can get my hands on the 9210!