Serialize An Object, Exception Because Form Is Not Serializable

I have a class called Truck and a form called frmTruck I have some code like this in a method. It recieves obj as Truck

Dim ms As New MemoryStream(1000)
Dim bf As New BinaryFormatter(Nothing, New StreamingContext(StreamingContextStates.Clone))
bf.Serialize(ms, obj)

To simplify my code, I have basically something like this for frmTruck:

public class frmTruck
private truckValue as Truck
public sub DoSomething()

[code]....

During the LoadTruckFromDatabase function I call the SerializeTruck method, here everything goes fine. But when I call the SerializeTruck just before End sub of DoSomething, it goes wrong I get an exception saying that frmTruck is not serializable My truckinstance doesn't have any references to frmTruck...