Failing to execute Sweep2rail component

I am trying to make a free formed surface by using the "Swp2" component in Grasshopper.

But for some reason, I can not do that. In Rhino I can create that free formed surface using "Sweep2" command, but not in Grasshopper. For some reason, the problem lies withing the second cross-section curve. Every time I load it into the "curve" parameter, "Swp2" components quits working.

Any suggestions, why is this happening?

Thank you.