I was painful (& nearly re-install the Ubuntu; Natty) with this problem more than one month, trying to find what is cause this problem.
The problem is when you open/use an application which need an authentication (a authentication window pop-up) the window just opened and shake shake, say that your password was not correct but you didn't have chance to input any password.
This screenshot I took by quickly press PrtScn button.
We can found the error message of this error in /var/log/auth.log. message look like this "...gnome-keyring-daemon[1423]: couldn't allocate secure memory to keep passwords and or keys from being written to the disk..".
Solution:
Need to change a following file's permission: /usr/lib/policykit-1/polkit-agent-helper-1
by execute this command in a terminal.
sudo chmod +s /usr/lib/policykit-1/polkit-agent-helper-1
found from > http://ubuntuforums.org/showpost.php?p=10620872&postcount=9