Pat I know it gets frustrating believe me I was the same way as you are right now a few yrs ago when I started to promote Referback and like Dom says it takes awhile to get off the ground with them but when you do they will retain your players for years to come.
I think that since they are such a great program that many of the seasoned affiliates have promoted them so much before you and they have attracted many of the players, this group has been massively exposed on the net over the years and there are many players that already have accounts. I would suggest trying new seo tatics and try to target a specific group of players with carefully chosen keywords etc.