convert to sheet metal

Hi,

I've imported 2 parts from a step file. I'm able to convert 1 file (3.2a) to sheet metal and unfold it. The other part (B045-T023-T024-B_0) is unable to convert to sheet metal. I even can't start a sketch on the faces. Has anyone an idea how i can convert this into sheet metal, or any reason why this isn't possible?

Important: I've a few thousands to make, all different lengths. So redrawing is not really an option.

Thanks!

SolidworksSheet Metal