Problems creating a custom object from script

My appologies in advance for cross-posting this, but this is driving me nuts. I'm using the starter.racing example as a foundation for starting my own project.

I have created a class derived from Vehicle, and haves exposed it to the Console using the DECLARE_CONOBJECT and IMPLEMENT_CO_NETOBJECT_V1 macros.

I create the class using the following Script code;

function GameConnection::createTank(%this, %spawnPoint)
{
	if (%this.OpHoverTank > 0)  
	{
		// The client should not have a player currently
		// assigned.  Assigning a new one could result in 
		// a player ghost.
		error( "Attempting to create an angus ghost!" );
	}

       // Create the player object
	%tank = new COpHoverVehicle() {
		dataBlock = HeavyTank;
		client = %this;
	};

	MissionCleanup.add(%tank);

       // Player setup...
	%tank.setTransform(%spawnPoint);
	%tank.setShapeName(%this.name);
   
        // Update the camera to start with the player
	%this.camera.setTransform(%tank.getEyeTransform());

       // Give the client control of the player
	%this.OpHoverTank = %tank;
}

However...when the mission starts and I go to the console, I get the following error

Game/server/scripts/game.cs (341): Register object failed for object (null) of class COpHoverVehicle.

I don't have a clue as to what I could be doing wrong to get this error. Can anybody point me in the right direction?