Not sure what the secret is... I just said that I was trying to book a routing and it wasn't coming up, then the agent looked into it and said oh, its the correct fare so it should show up... please hold and I'll have it booked.
The other situation is with the Reserve companion cert for F. That one never seems to work correctly for me. It shows different flights with successive searches (randomly depending on the phase of the moon, temperature etc), then coughs up with some error code when I've tried to book. End up calling and they do it.