Today, I was upgrading a SharePoint 2013 development server that had been “laying low” for a while to Service Pack 1. The installation itself went without any problems – I downloaded the SP1 executable from Microsoft and ran the installation.

After the installation, it was time to run the SharePoint Products Configuration Wizard, and I encountered the following error in step 8: “Failed to install application files”. In more details, the exception in the log file was:

Failed to install the application content files.

An exception of type System.NullReferenceException was thrown. Additional exception information: Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.SharePoint.Administration.SPAspConfigurationFile.ApplyActionToXmlDocument(XmlDocument xdAction, XmlDocument xd, String sourceFileName, SupportedXmlDocutmentActions supportedActions)
at Microsoft.SharePoint.Administration.SPAspConfigurationFile.MergeWebConfig(XmlDocument xdWebConfig, String fileMask)
at Microsoft.SharePoint.Administration.SPWebService.ApplyApplicationContentToLocalServer()
at Microsoft.SharePoint.PostSetupConfiguration.ApplicationContentTask.Run()
at Microsoft.SharePoint.PostSetupConfiguration.TaskThread.ExecuteTask()

The messages clearly says that there is a problem with a web.config file (“ApplyActionToXmlDocument” and “MergeWebConfig”). I have 8 web applications on the development server (most are closed down), and by looking at the web.config files in the web application folders under C:\inetpub\wwwroot\wss\VirtualDirectories I discovered that one of the web.config files had not been updated during configuration (the “Date modified” was not updated). Inside this web.config file I had a row that was commented out, as in the image below. After removing this row, I was able to run the configuration without any problems.