[Twisted-Python] Magical Disappearing Transport

[Linden Wright]

Hi -
I have a client factory and protocol written for TCP connections, and 
whenever I try to transport.write(), it tells me that the transport == 
None. The only time that I can successfully transport.write() is in my 
protocol's connectionMade method. My protocol inherits from 
protocol.Protocol, my factory inherits from protocol.ClientFactory, and 
otherwise, my code pretty much follows the examples.
What causes the transport to be set to None?
I feel like I'm missing something very basic, and I'm new to twisted, 
so I probably am. =)
Thanks,
Linden