That seems like a tough challenge, wish i could help you. Maybe if we keep the thread going long enough someone with experience in these things will stop by...I know some people have gotten PowerPak carts to work on RetroDuo without any hastle, so if you get different error messages for each CF but both of them work in the NES it sounds like the CF is the problem.

Can someone post their brand of CF that works on the RetroDuo? It sounds like doing that--and making sure you have the current software on the PowerPak--should do the trick.

Good luck