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

"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"

Cause :By default the files are designed to open in browser. So it will check for trusted location

solution :Follow the below steps.

1. Go to the Library
2. On the top click on Library and go to Library settings .
3. Under General settings you will find Advanced settings
4. Over there you will find the option which by default is set to open in Browser
5. You need to set it to Open in Client and there you go .
6. Click OK to apply the settings.

• See more at: http://expertsharepoint.blogspot.de/2013/10/error-when-open-excel-files-in_22.html