rebuild errors, you must select a fixed planar face or a liner edge on an end face of a cylindrical face

I am trying to draw a rectangle to round transition in Solid works 2015. I have one side sketched out then I skin it and try to convert it to sheetmetal but I get the above error. What am I doing wrong?? This should be easy, but I am having no luck

Thanks

Rob

SolidworksSheet Metal