[ODE] collision-based error messages

[John Rieffel]

Hi Folks,

since switching from ODE 0.5 to 0.7, I've been encountering the  
following error continuously dumped to my screen, but only when  
collisions are enabled in my system:

ODE Message 2: vector has zero size in dNormalize4()

This seems to occur whenever two parallel flat surfaces collide   
(most often one of those surfaces is the floor).  Capped cylinders,  
for instance, produce no errors when colliding with each other,  but  
do when they lay flat on the floor.  Switching from cylinders to  
boxes doesn't change anything.

This occurs with MAX_CONTACTS set to 20, and at all step sizes i've  
tested, from 0.1 to 0.005.

My nearcallback is copied verbatim from the boxstack example, as is  
the code which produces my cylinders.

any suggestions?

John Rieffel
Cornell University