TweenCrv component failure in grasshopper

Attempting to use TweenCrv, but running into a failure I can’t seem to diagnose. I get the runtime error “1. Tween could not be computed [step:1]”. Two curves as inputs, factor set to .5. Any ideas?

If possible, please post your curves here, so that other people can look into your specific problem.

Thanks. I rebuilt the curvesprior to TweenCrv and it worked like a charm. I believe it may have been getting confused by some self-intersection or some other anomaly.