Motionblur renderings doesent start with Railclone

Hi,

i have a large scene with a camera fly through. I am using Railclone and forestpack as plugin.

When i use Motionblur the renderings does n?t start.(updating instances). The same when i try to render a velocity pass as post blur solution.

RAM does n?t seam to be the problem, vray is using 16 gb of 32 gb. Any idea?