Today I was looking into Excel Services REST API (ExcelRest.aspx) in SharePoint 2010 for the first time. I followed some good articles on the web but kept on getting HTTP 403 Forbidden errors when invoking ExcelRest.aspx through the browser. Surprisingly didn’t find much help on this error on Google.

Looked into the ULS and found the following error message:

Result=Microsoft.Office.Excel.Server.CalculationServer.ExcelServiceBase+EcsFaultException: This workbook cannot be opened because it is not stored in an Excel Services Application trusted location. (Fault Detail is equal to Microsoft.Office.Excel.Server.ExcelServerMessage).

This must be one of those rare occassions that SP gives you error messages that help troubleshooting!

To fix this launch Central Admin, then go to Manage service applications, and click on Excel Services Application. Click Trusted File Locations and then add your location as a Trusted File Location.