ApplicationPoolIdentity doesn't have write permission to ASP.NET App_Data folder

This article helps you resolve the problem that an error (access denied) occurs when a web application writes data to the ASP.NET App_Data folder.

Original product version:   Internet Information Services 7.5 and later versions
Original KB number:   2005172

Symptoms

A web application is created using Microsoft Visual Studio and then published to Internet Information Services (IIS) 7.5 or a later version. As part of the application's request processing, it needs to write data to the App_Data folder on the server. For example, the application uses a SQLDataSource or XMLDataSource. When it attempts to do so, an error message similar to the following is displayed:

Exception Details: System.UnauthorizedAccessException: Access to the path [path to App_Data folder] is denied.

Cause

Beginning in IIS 7.5 and later versions, the default identity for an application pool is ApplicationPoolIdentity. When a web application is created using Visual Studio, the App_Data folder is not automatically configured to allow write access for ApplicationPoolIdentity. Therefore the attempt to write to the App_Data folder will fail.

Resolution

To work around this behavior, grant both read and write ACL permissions to the ApplicationPoolIdentity (IIS APPPOOL\ApplicationPool) on the App_Data folder.

More information

ApplicationPoolIdentity is a managed service account, which is a new concept introduced in Windows Server 2008 R2. For more information on managed service accounts, see What's New in Service Accounts