If you happen to be the system administrator and you’ve turned to google bing google to find the answer hopefully this blog post will help you out!
I believe this error is most likely if you are going over SSL as the default trusted location is just http://
Jump into central admin (please ignore my heath analyzer!) and goto Manage service applications.
Click on Excel services Application.
Then click on “Trusted file locations”
You can see that http:// is already there, so you could just add https:// or put in a url to a specific location
Fill in the boxes, I also ticked the trust children box.