Hi John,
Thanks for the details. Firstly your site is responding extremely slow I can't actually gain access after waiting for it to load for around 6 minutes it's still 'Waiting'.
I am going to suspect it's mainly your web hosting at fault, a 406 error tends to be a server not accepting the content type. I'll try again later, but at present we cannot access your site.
--Update, your site finally loaded after 10 minutes, but on trying to login it was then doing the same thing. We cannot debug it when we are waiting 10 minutes per page to load.
Many thanks
Tony