Revit cannot attach to the chosen Roof/Slab. The truss cannot project to a surface or the attachment creates an invalid profile.

public static FailureDefinitionId TrussIsAttachedTo { get; }

Public Shared ReadOnly Property TrussIsAttachedTo As FailureDefinitionId
	Get

public:
static property FailureDefinitionId^ TrussIsAttachedTo {
	FailureDefinitionId^ get ();
}