OK, I've solved it. The issue with display_as location remains and I still have to put the Allow from directives in the / location but I have been able to get UCSC working again and I'm completely to blame so maybe I should keep quiet but no, in the spirit of sharing one's idiocy here it is folks.
I was looking at user account admin a few weeks back and noticed some old users before I switched to the AD authentication so I thought it would be a good idea to clean them out. Turns out there is an account called remote_display_server which I had deleted and that was the key because removing that triggered the user_disabled message that UCSC was seeing (duh!) so re-enabling that fixed the issue (double duh!)
I will now sit in the corner with a dunce cap on for the rest of the day.....
Shane
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Dr Shane Sturrock
Senior Scientist
Tel: +64 (0) 9 379 5064
76 Anzac Ave
Auckland
New Zealand