Hi All,  am trying to create an edge flange off an already existing edge flange in a sheet metal "box". The box was created by defining a box sketch as the base flange, adding edge flanges to all four top, outside edges then creating welded corners. The edge flange tool is now completely locked out! Why might this be?

I have the part file attached if anyone might know what's up. Note I am using Solidworks 2015 so I have a JPEG in there as well.