Don’t know for sure if this is your issue, but we got the same error once in a while on a couple of our nodes and it was driving us batty because it was hit or miss.
The two things we did that stopped those “not responding” errors was this:
1. Make sure all materials and bump/disp map images are accessible across your network to all nodes. (find a common folder for everything/ The complex models have so many maps it’s easy to have one that is unreachable.) I think it is suppose to push them from the main to the nodes, but if one map is overly large, this may slow that down.
*2. Make sure you turn off the sleep functions of your nodes. We noticed a couple of the render nodes going into sleep mode and they wouldn’t wake up when Vray requested them to, at least not fast enough…because they had to wake up first-if they did at all. Usually after this happened we had to restart the node, try again, and it would work fine.
Like I said, not sure if this is your issue, but it helped us stop that from happening.
So tune the render nodes to run full bore, turning off any sleep/hibernate settings.