I keep getting a 'Type XXX is not marked as serializable' exception when I try to serialize an object of mine. It might sound silly, but my problem is that I can't seem to find any references to an object of type XXX anywhere on the object graph (using the debugger hover windows). Does anyone know a good way to scan the object graph for anything of this type?

It's a complex object graph (100s of levels deep), so I'm sure that some there must be a field of tye XXX somewhere, but I just can't find one.