Site Permissions – Object reference not set to an instance of an object

Recently had a strange experience with a client site. Clicking on Site Permissions caused this error:

“Object reference not set to an instance of an object”

I was also getting an error when backing up thru Central Administration:

“The Default Zone of this Web Application has no associated IIS Web site.”

Somehow the Default Web Site in IIS was being used for SharePoint instead of SharePoint – 80. To fix this:

1. Unextend all the Web Applications  (do NOT check delete web site for Default Web Site).
2. Extend SharePoint – 80
1. Use Port 80
2. Use standard virtual directory path