Drop all active database connections failed for Server when executing KillAllProcesses - sql-server

Question

I need to perform a database restore from my application. Before doing this, I want to kill all processes as follows:
private void KillAllProcessesOnSMARTDatabases(Server targetServer)
{
targetServer.KillAllProcesses(SMART_DB);
targetServer.KillAllProcesses(SMART_HISTORY_DB);
targetServer.KillAllProcesses(SMART_METADATA_DB);
SqlConnection.ClearAllPools();
}
However, when the first KillAllProcesses is run, I get the following exception:
Microsoft.SqlServer.Management.Smo.FailedOperationException: Drop all active database connections failed for Server 'MYServer'. ---> Microsoft.SqlServer.Management.Common.ExecutionFailureException: An exception occurred while executing a Transact-SQL statement or batch. ---> System.Data.SqlClient.SqlException: Only user processes can be killed.
The connection string used to create the server has sa credentials, however, the processes that need to be terminated are started under a different user. I tested the similar scenario and the test succeeded.
This started happening only recently. To me it appears there are some processes running that are not started by the user?

Answer 1

It would appear that your code is attempting to terminate all SQL Server Processes, which is not a good idea.
If you want to perform a database restore, you should set the database in question into either single_user mode or RESTRICTED_USER mode, the later being the most suitable.
Take a look at the following example of switching a database to RESTRICTED_USER mode and how to close any open user connections in the process.
How to: Set a Database to Single-User mode

Answer 2

You can use SMO to "kill" a particular database.
This will force a drop of all client connections to that database only and then drop the database itself.
Microsoft.SqlServer.Management.Smo.Server oServer = this.GetSmoServer();
oServer.KillDatabase(this.DatabaseName);