With SharePoint 2010, you might run into an issue when attempting to create a new PowerPivot Gallery Document from PowerPivot gallery, like this:

 If you encounter this issue, you may then see the following to errors:

The reason for the error is that SharePoint is looking for the template .xlsx file in the wrong location.

To resolve the issue:

1. Navigate in SharePoint to your PowerPivot gallery
2. Click on the Library menu at the top (like below)
3. Click on the Open with Explorer icon (like below)
4. Move the Forms folder that is located there into the ReportGallery folder, or if the Forms folder does not exist, create a Forms folder in the ReportGallery folder (like below)

Now the path to the template.xlsx folder will be correct, and you shouldn’t get any errors when creating new PowerPivot Gallery Documents from PowerPivot gallery.

You might see a scenario where data refresh with PivotTables or slicers or Data > Refresh All Connections are not working, and you are seeing an error in the browser like this:

 You may also find a corresponding error in the SharePoint logs like this one:

“MossHost.TryGetWindowsIdentity: Current identity is ClaimsIdentity. We need to get a WindowsIdentity”

With PowerPivot workbooks viewed in the browser via Excel Services, in order for PivotTables or slicers or Data > Refresh All Connections to work, the C2WTS is utilized. If the C2WTS is being run by a domain account (Microsoft recommended best practice), then that domain account needs a few certain permissions on each of the SharePoint servers where it is running:

1. The C2WTS domain account must be in the local Administrators group on the SharePoint servers where C2WTS is running
2. For the SharePoint servers where C2WTS is running, in the server’s local security policy, the C2WTS domain account needs these permissions:
1. Act as part of the operating system
2. Impersonate a client after authentication
3. Log on as a service

To access a server’s Local Security Policy, go to Start > Administrative Tools > Local Security Policy > Local Policies > User Rights Assignment

If you do add any of the permissions above for the account that is running the C2WTS, then you will need to restart the C2WTS on each of the SharePoint servers where it is running.

If the account that is running the C2WTS is LOCAL SYSTEM (not recommended), then no further permissions are required.

The following applies to SharePoint 2013:

1.   Restarting ECS will force a wipe and reload of PowerPivot databases.

2.   Any service account needing to interact with the PowerPivot data model needs to be an Administrator on the PowerPivot AS instance.  This is less obvious when you are in a client application but consider these scenarios:

              a.   PowerView client (in Excel) > SQL Reporting Services service application needs to be an admin

              b.   Performance Point > Performance Point Service application needs to an admin

3.   This table shows backward compatibility for workbooks in SharePoint 2013 and what service application performs a scheduled data refresh.  Interactivity refers to the user-level interactivity allowed with the PowerPivot data model.  Only Excel 2013 workbooks allow for full permissions, which equates to full back-end connection-based data refresh in browser (which means writing/updating the data model in PowerPivot-AS):

* Note:  Data refresh schedules for PowerPivot 2012-Excel 2010 workbooks, the PowerPivot System Service account requires modify rights to the workbook in SharePoint as well as admin rights on the PowerPivot-AS server.