SharePoint 2013: this workbook cannot be opened

Problem

You have newly deployed an Internet-facing SharePoint farm.  A user reports that he is unable to open an Excel spreadsheet stored in a folder at this farm.  On clicking the filename in the SharePoint folder, the user sees this error: This workbook cannot be opened because it is not stored in an Excel Services Application trusted location...

Creating a new instance of the Excel Services Application automatically configures a default trusted location of http://. This works fine for internal, non-secured web applications.  However, this won't work for secured Internet-facing deployments, for which you need https://.

Solution

1. Launch Central Administration as farm administrator.
2. Go: Application Management > Service Applications > Manage service applications.
3. On the Manage Service Applications page, look for your farm's Excel Service Application listing, and click on this.
4. On the Manage Excel Services Application page, click Trusted File Locations.
5. Click Add Trusted File Location. and complete as desired.
   
6. Click OK.  The change will take affect immediately.

References

• Plan Trusted File Locations in SharePoint Server 2013
• Manage Excel Services trusted file locations (SharePoint Server 2013)