Console error...

I'm having a problem (this is my first attempt at implementing a new class in Torque) in that the engine does will not create an instance of a class from script. I create the class with the following method;

%tank = new COpHoverVehicle() {
        dataBlock = HeavyTank;
	client = %this;
    };

Only to get the following error;

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

I've registered the class a con object (it is derived from Vehicle) using the DECLARE_CONOBJECT macro in the class decleration and the IMPLEMENT_CO_NETOBJECT_V1 macro in the module file.

I don't suppose anybody has an idea as to what I might be doing wrong?