I've been pulling my hairs for the past 2 days.  For some reason, I can't do lofted Boss/Base with my design.  I know I'm missing something but I can't figure out what that is.  I'm trying to draw this RC wing but it won't let me loft it.  Either can't build error or some other error.  I can only use one of the guidelines to loft it.

The second I added the second guideline in front, the shape of the loft change to this.

Can someone help point to me what I miss that caused the drawing to refuse to loft.  Please help?  Many thanks in advance.