"Requires to install untrusted updates" Error in Update Manager
In the software centre go to edit and software sources (type in your password) one of your software sources in the other sources tab does not have a key.
This does not necessarily mean it is bad but that you would need a key
Check this url:
http://www.liberiangeek.net/2010/10/fix-requires-installation-untrusted-packages-error-ubuntu-10-10-maverick-meerkat/
This will help you to resolve the error.