Parting surface icons grayed out??

I am working in Mold Design to create a Mold Cavity. I created the file and assembled a reference piece and then created my workpiece. I did a reference part cutout of the part from the block too, but not sure if that has relevance here. Anyway, when I open "Parting Surfaces" I am unable to select the "Extend Curve" tool. I tried unblanking and blanking both components and selecting a curve, but for some reason I cannot get it to be selected. The picture is shown below of the problem. 

I have been able to create Parting Surfaces using the Extend Curve tool before and am unsure why it isn't working now. Any thoughts? Please help!