Hey his is kinda of hard to explain but

This is kinda of hard to explain but, I am trying to make a lofted boss that starts with a circle of a diameter of 2cm and ends with circle of 0.5cm and it goes along a guide curve which is a helix, the helix is tapered along 3 degrees and pitch is 10cm and has 1 revolution.

I don't understand why it does not let me do this I keep getting an error message "loft operation failed to complete"

Thank you