what could screw up login credentials?

[Tom Horsley]

I had a working minimal install of f19.

I booted f18 on the same machine to get work done,
and in background installed a gazillion packages
while chrooted into the f19 partition.

Now when I try to boot f19, it tells me I have
an invalid password for every user I try to login
as :-(.

I tried chrooting in again and running passwd to
update the passwords, but it still says invalid.

Anyone know how the devil to fix this?