I once got this error because of a missing texture file.  I only figured it out beause in the bit that rendered, a figure was missing part of a texture.  I don't recall the details as to why it didn't ask for it when I loaded the scene...

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The Wisdom of bagginsbill:

"Oh - the manual says that? I have never read the manual - this must be why."
“I could buy better software, but then I'd have to be an artist and what's the point of that?"
"The [R'osity Forum Search] 'Default' label should actually say 'Don't Find What I'm Looking For'".
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