Lost player

I was preparing the SBC challenge in FC Companion, specifically the Cold Moon challenge. When I added the players and pressed send, I got an error. I exited the program and reopened it, but one of the players I had added had disappeared. When I searched for him, I couldn't find him, and the challenge wasn't completed. The next day, I tried the challenge again, and the same problem occurred. I don't know why, and my players still haven't returned.