Swept boss with variable pitch and diammeter

Hi

I am trying to make a spring like object which has a variable pitch and diammeter, ive created the Helix/spiral, and would normally draw a circle on the end and sweep it along the profile of the helix, however no matter what i do it just wont do it, but also doesnt give a reason for it

Thanks for any help

Regards

Chris Freshman

SolidworksParts And Features