Mental ray render error "degenerate trimming loop"

Example
GAPT 0.11 warn 092052: degenerate trimming loop

Before mental ray tessellates a trimmed surface, its trim curves are checked. Duplicate verticies as well as overlapping edges are removed. If, after this process, a trim curve contains less than 3 verticies, the 'degenerate trimming loop' warning is issued and the entire surface is skipped over.

Use File > Optimize Scene Size and toggle on "Remove Invalid Nurbs Surfaces and Curves" to clean this up.