when using WRS :PTC.CADDocumentMgmt.GetStructure service throws error for some assemblies

for getting CAD Structure of assembly, we are using the service  /CADDocuments('{CADDocumentId}')/PTC.CADDocumentMgmt.GetStructure and adding the $expand=Components($expand=CADDocument($select=Name,Number,Version,State,TypeIcon);$levels=max)

for some assemblies its giving the desired results but for some assembly it throws error in WRS response as "OData Library: An exception without message text was thrown.".

can anyone help me resolve this issue.