Hi Simon,
I was trying out the demo version in max 2010 x64 with VRay 1.5sp4a. Whenever I drag out a new connection to any properties of a VrayMtl (vray material) I get a .NET exception. Seems to happen on any of the inputs but dragging a bezier float controller to the diffuse value is one concrete example.
This was fixed in the latest build (which was just posted an hour ago or so) which you can get if you download/install the demo again. VRayMtl has some issues it seems (its the only material that does so) and we're trying to resolve them, though many patches are work-arounds.
Not a bug, but another problem is that the vray mtl ends up huge in the schematic view as all the inputs show up in one huge category. Not sure if there's anything you can do about that though.
We're currently working on cleaning these up.
Cheers
Marsel Khadiyev (Software Developer, EPHERE Inc.)