I have seen this before and it turned out to be a corrupted file in
/tcb/files/auth/[a-z]*

Look around in those directories for large files. Viewing a few files
will show you what is normal and abnormal.

You can try to use the 'authck' command which might fix it, but you'll
probably need to manually edit any corrupted files you find.

Always have a recent backup on hand, and always remain logged in as
root somewhere until you've completed any repairs.

Also read the pwconv man pages, as well as authck, passwd and shadow
pages.

Good luck,
Mark