Disable shaders.
Won't help.This is a known bug with v21.
I get the error only with shaders enabled. So it clearly helps me if I disable them.
Place an emitter on a brick. Anything that involves emitters causes it too.
Read the bugs topic by Badspot.This is just console spam that everyone is having and Badspot can't figure out the cause.Bugs topic:2012/08/10 - Bugs