public void Error()
{
PartDocument oDoc = (PartDocument)oApp.Documents.Add(DocumentTypeEnum.kPartDocumentObject);
PartComponentDefinition oCD = oDoc.ComponentDefinition;
PlanarSketch sketch = oCD.Sketches.Add(oCD.WorkPlanes[1]);
TransientGeometry oTG = oApp.TransientGeometry;
SketchLine line1 = sketch.SketchLines.AddByTwoPoints(oTG.CreatePoint2d(1, 1), oTG.CreatePoint2d(2, 2));
SketchLine line2 = sketch.SketchLines.AddByTwoPoints(oTG.CreatePoint2d(-1, -1), oTG.CreatePoint2d(-2, 2));
sketch.GeometricConstraints.AddCoincident((SketchEntity)line1.StartSketchPoint, (SketchEntity)line2.StartSketchPoint);
// можно, конечно, вот так заморочиться
// sketch.GeometricConstraints.AddCoincident((SketchEntity)line1.StartSketchPoint, (SketchEntity)line2);
// sketch.GeometricConstraints.AddCoincident((SketchEntity)line1, (SketchEntity)line2.StartSketchPoint);
}