Error:

(While extending an IIS site with FrontPage Server Extensions): "An internal error occurred processing the quota information."

Solution:

• Confirm application pool (usually MSSharePointAppPool) is started/functional, and that it is running under the Local System identity.
• Sysinternals' Process Monitor may also help identify which files are causing problems - check permissions on roles.ini, and other files located in Documents and Settings\All Users\Application Data\Microsoft\Web Server Extensions\50.
• Stop using Frontpage extensions. =)