I've performed an upgrade to 4.8.2, but now no users can log in. I can get to the login page, but authentication fails. If I try to have it send my password, it says:

There was an error retrieving your password. No password was sent.

I know all my users are still there, I can see them in the database. Is there an easy way to reset or retrieve passwords, or is there something else going on?

I did make backups! Changing the machinekey worked for almost all. One that doesn't is the host account. I tried the fix here: http://www.deutschnetnuke.de/tabid/183/Default.aspx

But host still cannot log in.

I'm having the same problem.  Is the machine key just one line, or do I need to replace a whole section somewhere?