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

[ComradeP]

The .cpf files are files for the campaign, which are loaded through a seperate boot program (cp_start.exe in the BoN folder or Campaign Game shortcut). The .cpf file is the file you're supposed to send to your opponent, and open when it's returned.

The normal game files are .bte files, which can be opened in the main program (BoN.exe or Main Program shortcut).