That normally means that there is a "kink" or sharp corner in your curve. From the look of that it is very small kink, but still a kink.

This probably happened by joining together 2 curves that didn't have an exact tangent alignment.

The easiest way to fix it is to turn on points for the curve, and select the point at the kink and delete it. This will be the endpoint of the segments that were joined together. When you delete that corner point MoI will merge the 2 segments together into one smooth segment.

- Michael