When CompoundStructure::isValid() returns false, it uses these values to indicate precise nature of defect. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 16.0.0.0 (16.0.0.0) 
  Since:  2012 
Syntax
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Members
| Member name | Description | 
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| BadShellOrder | Layer Function Priorities ascend from the Core Boundary to the Finish Face. | 
| CoreTooThin | Core contain a membrane layer or thickness of core is zero. | 
| MembraneTooThick | Thickness of membrane layer is more than zero. | 
| NonmembraneTooThin | Thickness of non-membrane layer is too thin. | 
| BadShellsStructure | The number of shell layers is larger than the total number of layers. | 
| ThinOuterLayer | Thickness of face layer is too thin. | 
| VerticalUnusedLayer | A layer is not membrane layer and the Thickness of layer is zero. | 
| VerticalWrongOrderLayer | Layers assigned to the same Row are not on the same side of the Core Boundary. | 
| VerticalWrongOrderCoreExterior | Exterior core boundary have more than one face at any height. | 
| VerticalWrongOrderCoreInterior | Interior core boundary have more than one face at any height. | 
| VerticalWrongOrderMembrane | Membrane Layer have more than one face at any height. | 
| DeckCantBoundAbove | There is no layer above Structural deck or it is too thin. | 
| DeckCantBoundBelow | There is no layer below Structural deck or it is too thin. | 
| VarThickLayerCantBeZero | Variable thickness layer have zero thickness. | 
| InvalidMaterialId | Element id used as material id does not correspond to an actual MaterialElem. | 
| ExtensibleRegionsNotContiguousAlongTop | Extension Layers at the top of the wall must be adjacent. | 
| ExtensibleRegionsNotContiguousAlongBottom | Extension Layers at the bottom of the wall must be adjacent. | 
| InvalidProfileId | Element id used as profile id does not correspond to a valid deck profile. | 
Remarks
 'LayerTooThin' enum value was removed in 2016