I'm pretty sure this started when I went from SW2010 to SW2012.  When I place a sketch entity in a drawing view, restrain it, then place a dimension, I get these error messages.  In the picture below I placed sketch lines to show ground level on this curb (I could have placed a surface in the model, but of course surfaces don't show up in section views).  The same thing happened when I placed a sketch point coincident with the top edge and right face so I could place the 8" dimension.  I don't think it hurts anything but it is annoying.  Any ideas?