A tricky one, the problem was that there were 2 radii 0.0001 in size - I have attached a modifed drawing and machining program.
When I come across a problem like this I always suspect the original geometry.
Finding the problem is the key, what I did was this:
In CAM switch on Number Spans from the View Options menu - right click the mouse in the graphics window - then on the Goround dialogue select the Options tab and set the end span to say 50 - then run the job, if Ok then I know the problem is further on, did again to 60 - Ok, then again to 70 - problem, so then reduced the number to 65 - ok and so on.
It's a bit long winded but it's only way to narrow down where the probelm lies.
Having found the problem - in CAD deleted the arcs and used Intersect with Clip to trim the lines so that they meet. Recreated the contour and bob's your uncle !