“This workbook cannot be opened because it is not stored in an Excel Services Application trusted location. To create an Excel Services Application trusted location, contact your system administrator.”
If you happen to be the system administrator and you’ve turned to googlebing 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.
Now, You should be able to open the Excel workbook from your sample excel report in BI center of Project server.