updated ubuntu, password no longer works

Help.

In one of my linodes earler this evening, I updated ubuntu with apt-get dist-upgrade. I rebooted the machine after that.

Now, when I telnet into linode, them move over to that box, when I try to log in, it doesn't work.

I had two user accounts on that system; I have the password for each stored in a password manager, and I'm copying and pasting.

Neither works.

It's a mail server, and I'd really like to try to fix this without restoring from a backup.

Any ideas?