If the FP system is in the scene I am rendering (Vray 2 SP1) I don't have any problems. Everything works great!
I seem to have consistent problems using XREF scenes containing the FP systems. I usually have my site and building files in separate file then XREF them into a master file for lighting and rendering. I can render the site files with FP grass, trees etc without a problem. If I XREF the site file and try to render, Max sort of hangs. Hard to describe exactly. I can save and close the rendered Vray frame buffer, but I cannot interact with Max in any other way. I have waited 15 minutes for Max to come back to life, but I end up killing the Max process and relaunching the APP. This happens with various files with FP systems.