I have encountered the error "Call to Excel Services returned an error" when performing a Scheduled Data Refresh.
In several cases, this has been because the PowerPivot connection is using the "SQL Server Native Client" Provider. We recommend that you use our enterprise Provider "Microsoft OLE DB Provider for SQL Server". I assume the reason why many workbooks are using this is because these workbooks are created on a user's desktop machine. I assume the reason why this fails is because the server does not have this provider installed.
To check and see what provider you are using Open Excel > PowerPivot tab> Manage
Design > Existing Connections
Select the appropriate PowerPivot connection> Edit
Change the Provider from "SQL Server Native Client" to...
"Microsoft OLE DB Provider for SQL Server"
Important Note: Click "Test Connection" to ensure that the connection in the workbook is able to properly retrieve data. If is cannot retrieve data, then you will need to analyze the error it returns.