Campaign PBEM Bug? Human Error?

[Bbbuzzard]

Apologies if this has already been addressed, or if I'm just overlooking something obvious. 
I've played most of the Tiller titles over the years, and have never really had a problem with the email system. However, I've been trying to initiate a PBEM campaign in PzBN for a few days, and I'm clearly making some kind of mistake. 
Whenever I initiate and seek up attach the file to send, I'm only given the option of a .CPF file. I believe I'm supposed to use the .BTC file, but there is none. When I do open the file, it gives me an error message. 
What am I doing wrong here?  Thanks!
Buzz