Particle ~ Vertex Group Cuasing Crashes?

has anyone had issues whereby using a vert group in particles gives a TDR error? i’m modelling a panther at the mo, been combing the body fur (10000 hairs, 100 children in Render) and didn’t have much issue until today when i decided i wanted a tweaked hair system for the ears so i created the necessary vert group for the body’s Density setting, at which point every time i go into Rendered view, or try to F12, i TDR. remove the group, no probs.

test test test

test test test