Revit cannot attach to the chosen Roof/Slab. The truss cannot project to a surface or the attachment creates an invalid profile.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 25.3.0.0 (25.3.0.0)
Syntax
C#
public static FailureDefinitionId TrussIsAttachedTo { get; }