Profile Ribs - Question

I'm working on a part out of a text book right now, (Drawing attached). It is simply two surfaces connected on a 60 degree angle. I'm trying to add a rib profile from one surface to the other. I draw a simple line sketch and then the rib option tells me I can't intersect the part or various other cryptic error messages. I watched a couple of tutorials on it, and it seems pretty straightforward.

I guess my problem is in the open ended sketch. Any insights. greatly appreciated.

Thanks.