In my test-environment , i get following error, after log into cms
Refused to display 'http://cms.luctho.de/?1&iframe' in a frame because it set multiple 'X-Frame- Options' headers with conflicting values ('DENY, sameorigin'). Falling back to 'deny'.
Test-Environment: local virtual Server (Ubuntu) with virtual box. I added entry to etc/hosts to point on the local server. Site works fine and I can access the Url http://cms.luctho.de/?1&iframe without any issues.
Let me know if you need more information!