Hi
I've got the MSI Geforce GTX 1070 Armor 8G Oc graphics card and have the same issue.
What i did was, start the render with rt cpu mode then switch to rt cuda mode and it started working. Not sure if it's a compatibility problem or not. Wish someone could explain in full detail the specifications of the vray rt render and these issues with graphics cards.I´ve read that it's still very grainy and a bit buggy in 2.0 version but saw a video of a russian guy making spotless renders. I really don't know how or why.
Let me know if it solved the problem or if you managed to getting it to work from the start.