Boot the system to single user mode and run: #authck -a
If this does not clear the problem, then in single use mode, edit the following file:
/etc/auth/system/ttys
so that all the lines look like the following format
In the ttys file there should be one line for each configured terminal. You will have terninals named ttyp1 through ttyp99 if you have tcp installed. If you only have the 'host' version of the operating system then you will not have any.
Are you able to boot the system to single user mode?
Boot the machine to single user mode, then cd to /etc/rc2.d/messages and look at the log files from each procedure to see if there is any more information about the failure.
Worst case: if you mount all the file systems, you can do a backup of the entire system and re-install the operating system.