I haven't used the RIYA cards before, but I've seen similar issues when running multiples of other cards on occasion (network adapters and video cards come to mind!)
First, what operating system are you using, and do you have the latest updates for the computer hardware (motherboard & chipsets)? Also, I have seen cases where even though you move cards between slots, you could STILL be experiencing IRQ conflicts, or possibly even DMA conflicts.
If you're using Windows 9x / XP / Vista, open Device manager and make sure BOTH cards show up with no errors. If they don't, you might be able to tell what is conflicting from Device manager. You may need to go into the Riya configuration software (if there is any) or in lieu of that, change jumper settings on the cards (if there are any) to get rid of conflicts. And, as mentioned, make sure you have all the latest motherboard / chipset drivers for the operating system you are using.
Good luck !!
RR
Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
1979.
Sweet.....