The splitting boundary drawn would result in a self-intersection of the surface boundary. Please edit your splitting lines to correct the problem.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 26.1.0.0 (26.1.0.34)
Syntax
C#
public static FailureDefinitionId SurfaceSelfIntersection { get; }