NO IT IS NOT TRUE! You CAN run mix of AMD and NVIDIA cards within one miner.
Thanks for clarifying, as I was mining with 6x amd and 6 x nvidia cards with the one miner.
Just need to figure out what the problem is with my claymore!!! and why its crashing my pc and not detecting my CUDA devices and only mining with 3 amd devices disabled.
Back to basics: I hate to make any assumptions, but you say it was working? I was thinking maybe you don't have the Cuda software installed? ("nSight")