Sketch can't be Automatically Dimensioned - this is a prerequisite for Labeled Dimensions to work properly.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 26.2.0.0 (26.2.0.0)
Syntax
C#
public static FailureDefinitionId SketchCannotBeAutomaticallyDimensioned { get; }