Generating user instances in SQL Server is disabled. Use sp_configure 'user instances enabled' to generate user instances.

Recently I noticed that many of my ASP.NET applications that work with a SQL Server Express database that resides in the App_Data directory stopped working. The culprit error was "Generating user instances in SQL Server is disabled. Use sp_configure 'user instances enabled' to generate user instances.". I suspect that a SQL Server update went out that disables user instances. I have not been able to substantiate this suspicion yet.


SOLUTION:

The solution is to enable user instances with the following command:

sp_configure 'user instances enabled','1';

Disable user instances with the following command:

sp_configure 'user instances enabled','0';