Can't change password

Every time I try to change my password, I get the following error:

Sorry, the password you entered wasn't right.

Here's what I do:

1. Login and go to "My account"
2. Click on "Change Password" and new fields show up.
3. Fill out my current password under Password and the new password I want under New Password and Confirm New Password.
4. Click on "Update my info"
... and then I get the error. I know I am using the right password because I am able to login, so I'm not sure why that's happening.

I'm using Firefox 3.0.5, Windows XP Media Center.