I noticed this red line a while ago but I’m it sure what it means anybody a Idea? 
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It looks like a PLine for working with a reference image on the grid. Turning off the Floor will hide it, or if you look in the Draw palette settings under Left-Right (or possibly Front-Back), turn off the PLine button.
You can read about the settings here:
http://docs.pixologic.com/reference-guide/draw/floor-grid/
and using the grids for refernce images here:
http://docs.pixologic.com/user-guide/3d-modeling/reference-images/grids/