You have selected elements that are already part of other System. They will be removed from the original Systems and added to this one.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 26.3.0.0 (26.3.0.0)
Syntax
C#
public static FailureDefinitionId SelectedElementsArePartOfOtherSystem { get; }