Here's another solution:
Click on Places, Home Folder. You will then need to hit
Control+H on your keyboard to view hidden files. (By the way, if
you want to always view hidden files, you can click on Edit,
Preferences and click the box in front of Show hidden and backup
files.) Browse to the folder called .gnome2, and then to the
folder called keyrings. Inside it is a file called
default.keyring. Delete it and the next time you enter a site or
mount with a password, it'll ask for a keyring password, and
then you can set a new one.