O.k., first of all, you didn’t do anything wrong, it’s a bug. I think it has already been reported (at least an other bug that is probably the same issue). I don’t know what is causing it, but I’m guessing that somewhere in the calculations of the Motion Blur, there is a division by the size or scale of the objects in the scene. When there are objects with size 0, that yields infinity and computers don’t like that and start misbehaving;)
You used a Colorramp in the Texture to control the Size of the Particles. The Colorramp had a black flag, and black means 0.
Being a genius, I changed the Value of the black color from 0 to 0.0001.
That is all! No more dividing by 0 and therefor no more infinity! Computer happy, we happy.
Took me quite some time to figure it out though, so maybe I’m not that much of a genius after all…:(
