"The line defining the axis is not valid" - Revolved Boss/Base

Hi all,

In the attached file, I'm trying to create a Revolved Boss/Base using "SKETCH Bottom Surface" as the Selected Contours, and "SKETCH Pattern Axis" as the Axis of Revolution. However, after I select the contour (no problems) and try to select the axis, SW gives me the error message in the title next to my mouse.

Anyone have any ideas/tricks as far as this goes ? All help is appreciated!

Thanks in advance,

SolidworksModeling And Assemblies