Proxy Profiles and AD SSO should make no difference.
When I worked on my Astaro from one PC, I received error messages also. When I worked from my laptop, I received no error messages. I deduced that the problem was with my PC.
Clear the browser cache on your PC: 'Tools', 'Internet Options', 'General' tab, 'Delete' Temporary Internet Files.
Reboot the PC, then it should work with your Astaro.
Saluti - Bob
Sophos UTM Community Moderator Sophos Certified Architect - UTM Sophos Certified Engineer - XG Gold Solution Partner since 2005