What is this surface?

Can anyone tell me what the triangular surface is in this model? I cannot delete it. Is it an ‘error’ or ‘bug’.Error.3dm (6.1 MB)

Hi Paul - that is a shading mesh ‘leaking’ out from the trim curves - start DivideAlongCreases set SplitAtTangents=Yes and then select the surface. Note the result will no longer be a single surface but a polysurface. Meshing and other operations should work better though.