Microfeed not working on Team Site - Internal error code 54

I installed a SharePoint 2013 farm using AutoSPInstaller. As usually the installation worked well. I then created a new Team Site site collection. The Newsfeed WebPart came up with an error message:

The operation failed because an internal error occurred. Internal type name: Microsoft.Office.Server.Microfeed.MicrofeedException. Internal error code: 54. Contact your system administrator for help in resolving this problem. 

  

First I checked the Distributed Cache. App Fabric Windows Service & Distributed Cache Service were running. The WebParts in MySite were working properly. So Distributed Cache Cluster should be ok. 

I checked the ULS and found the following error message, Level "Unexpected":

SPMicrofeedManager.CommonGetFeedFor: Exception System.Data.SqlClient.SqlException (0x80131904): The EXECUTE permission was denied on the object 'proc_Social_GetSecurityTrimmerEnabled', database 'SP2013_Social', schema 'dbo'. at System.Data.SqlClient.SqlConnection.OnError

Now it became clear that there is a permission issue. The application pool account of the Portal application needs additional rights.

I checked the properties of procedure "proc_Social_GetSecurityTrimmerEnabled" in the Social database:


SPDataAccess is the permission that gives the Execute right to the stored procedures. So I grant the role SPDataAccess to the Portal application pool account (here: SP2013_Portal) :


Refreshing the site collection the Newsfeed WebPart is working properly: