Okay, now I tested the other board I have.
It is a ASRock Z77 Extreme4 with 2 PCIE x16 slots, and 2 PCIE x1 slots.
Now here is what I found!
Latest BETA drivers install without problems.
1 GPU with raiser in the first PCIE x16, 1 GPU with raiser in a x1 slot: The miner crashes the driver.
1 GPU with raiser in the first PCIE x16, 1 GPU with raiser in the second PCIE x16 slot: The miner works!!!
What the actual F* ? 
Why won’t the RX470 work in a small PCIE x1 slot??