main/renderbuffer.c:2041: _mesa_add_renderbuffer:  assertion "bufferName ==
BUFFER_DEPTH || bufferName == BUFFER_STENCIL ||
fb->Attachment[bufferName].Renderbuffer == ((void *)0)" failed
This is due to an attempt to allocate a second front render buffer into the current frame buffer. This happens when calling calculate_buffer_parameters from viaMakeCurrent in mesa-6.5.2/src/mesa/drivers/dri/unichrome/via_context.c.