I can't flatten this

Hi,

I am trying to make this structure using sheets. In the absense of guide curve in the sheetmetal lofted bend option, I had to make it as a part first.

My guide curve is third degree polynomial. Now I can't flatten this using "Convert to sheetmetal" option.

Please help me out.

I also have attached the part in this post.

Thanks in advance.

SolidworksSheet Metal