While working with SharePoint 2013 PowerPivot, I got an error "An error occurred during an attempt to establish a connection to the external data source… " as shown the image below, while refreshing all the connections.
In logs I have found the error like, “Current Identity is Claims Identity. We need to get a Windows Identity”
We can view PowerPivot workbooks using excel services in browser. To refresh the data in power pivot tables, Claims to Windows Tokens (C2WTS) will be utilized. If C2WTS is running with a domain account, that account needs to have permissions to the SharePoint server. Account must be in Administrator for SharePoint server where the C2WTS is running and service should be run on the name of that account.
Check the account that running the C2WTS service and add “Act as part of the operating system” permissions to that account. We can find the account in services. (run ->services.msc)
To access the Server’s local security policy, go to User Rights Assignments (Start-> Administrative Tools -> Local Security Policy -> Local Policies -> User Rights Assignments)
The account running for C2WTS, need to add permissions for “Act as part of the operating system”