External users are unable to open documents from SharePoint, When a document is opened SharePoint asks for authentication and then loads the ISA connection screen in a word document.
I have attached the screen shot of this error.
If an external user users a VPN and then loads SharePoint everything loads ok. I believe this is a problem with ISA blocking connections to SharePoint. When setting up ISA I used a standard SharePoint publishing rule with no SSL.
Everything else works fine but opening documents.