I think I see what is going on then.
I added the www.domain.com
site and it works fine now.
I see in the Developers Forum there is a move to add a default site or page that is accessed by IP address. This is a good idea most certainly. Can I just add this to my Vhosts file in the meantime or could this cause a problem with ISPConfig and future upgrades. I saw your post in the ISPConfig roadmap on the topic.
I need to try FTP from a site outside my domain yet. Will advise if passive mode works.
Thanks for all your help.