Notice that this is now "failed to lock index buffer" rather than "failed to lock vertex buffer"
This seems to be happening under the same conditions as the vertex problem (almost randomly midgame), though this time I've only experienced it in Gmod. According to Steam support this happens when you alt+tab and don't have enough memory to render graphics or something, but the thing is I'm not alt+tabbing and I've set the heapsize to 1024000 kb (I have 2gb RAM). I'm at a loss ad to what is causing this. Help?