I've added the sites to trusted and the servicedesk guys has opened the firewall especially for these addresses but i still get the same error message.
Does it help if i say that i'm on a 8.5 server/publisher?
I don't remember how i solved it actually, but this problem occured again just a few days ago and then it was a proxy reason. The server had "forgotten" that the address was ok so to solved it i reloaded a couple of times until it worked again.
I found the solution to this issue. It comes from Windows internet options handling of mixed content. To fix it, open up "Internet Options" (from either the control panel or IE). Click on the "Security" tab. With the internet zone selected, click on the "Custom level..." button. Scroll down in the list for "Display Mixed Content" and select "Enable".
If you are running Win 2008, you'll need to disable IE Enhanced Security Configuration:
