Problem editing user/group settings

[Tom Taylor]

Tonight I tried to go into system-config-users to add groups to my user 
account I got the message:

The user database cannot be read.  This problem is most likely caused by a 
mismatch in /etc/password and /etc/shadow.

My question is WHY and how do I CORRECT it?

FC3t2 
kernel 2.6.8-1.541smp
KDE3.3

I want to do this so I can add groups to my user account so I can add devices 
to my user desktop.

TIA, Tom
-- 
Tom Taylor
registered linux user #263467