What Permissions Are Needed To Drop All Connections On A Database?

I'm looking for the correct permissions to grant a user the ability to be able to drop all connections on a database.

The following code throws an exception:

Dim srv As New Server(SqlServerName)

If srv.Databases.Contains(siDBName) Then
srv.KillAllProcesses(siDBName) '== the srv.KillDatabase will not work here, we must kill the processes first
Dim db As Database = srv.Databases(siDBName)
db.Drop()
End If

Throws the Exception:
Microsoft.SqlServer.Management.Smo.FailedOperationException:
Drop all active database connections failed for Server 'xxxx'.
The user does not have permission to perform this action.

This code DOES NOT throw an exception when run as an Administrator.
Any Ideas?