Join Vertices from merged curves? (What am I missing?)

I’m trying to connect one curve, hand-drawn, to another curve generated from a mesh. They’ve been joined together, but there’s something about the curves that prevents them from being connected into a continuous curve:

I can see that one of the curves is yellow without handles, the other black with green handles (or other colors, depending on various vertex types that I give it).

The only way I’ve been able to connect these is to Alt+C Convert to Mesh, then Alt+C Convert to Curve, at which point all curves are yellow, and I can connect them. I’d much rather know how to connect them without going through this seemingly unnecessary step. Any advice? Blend attached.

JoinCurveVertices.blend (626 KB)

One’s a poly curve and the other is a bezier curve.
Change the spline type in the toolshelf in edit mode under Curve Tools / Spline Type option

That’ll do the trick. Thanks as always, Richard!