Screensaver, can not unlock

Sometimes the screensaver will not unlock with a correct password.

Examining the /var/log/auth.log file shows error similar to the following:

Jul 14 19:04:34 desktop unix_chkpwd[1760]: check pass; user unknown

This is caused by the /etc/shadow file having the wrong permissions or ownership. Doing "ls -l /etc/shadow" should display the following:

-rw-r- 1 root shadow 1241 2010-08-22 12:43 /etc/shadow

if it does not, correct it so it does.