Something that had confused me the first time I tried Ubuntu Network
Manager was the wireless keyring. I had set it up without understanding
what it was, and after the first time I setup my wireless, it was the
keyring dialog that came up, which was an entirely different password.
That doesn't sound exactly like you describe, but just thought I would put
that information out there "in case". Otherwise, opening the network
manager and deleting the connections, then setting up fresh sounds like a
good option, as someone else suggested.