I am just upgraded my project to use the latest version of the zbuModelsBuilder facility to 2.1.1. (both within VS and the application). Rebuilt the application and am getting the following error. Am i missing something? Have used the builder in the past without an issue before.

ZbuModelsBuilder: ZbuModelsBuilder failed to generate code: Exception: Response status code does not indicate success (InternalServerError)

{"Message":"An error has occurred.","ExceptionMessage":"Common Language Runtime detected an invalid program.","ExceptionType":"System.InvalidProgramException","StackTrace":"   at System.Collections.Immutable.SecurePooledObject`1.Use[TCaller](TCaller& caller)\r\n   at System.Collections.Immutable.SortedInt32KeyNode`1.Enumerator.PushLeft(SortedInt32KeyNode`1 node)\r\n   at System.Collections.Immutable.SortedInt32KeyNode`1.Enumerator..ctor(SortedInt32KeyNode`1 root)\r\n   at System.Collections.Immutable.ImmutableDictionary`2.Enumerator..ctor(SortedInt32KeyNode`1 root, Builder builder)\r\n   at System.Collections.Immutable.ImmutableDictionary`2.GetEnumerator()\r\n   at System.Collections.Immutable.ImmutableDictionary`2.System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.CopyTo(KeyValuePair`2[] array, Int32 arrayIndex)\r\n   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)\r\n   at System.Linq.OrderedEnumerable`1.<GetEnumerator>d__0.MoveNext()\r\n   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()\r\n   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)\r\n   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)\r\n   at System.Collections.Immutable.ImmutableArray.CreateRange[T](IEnumerable`1 items)\r\n   at Microsoft.CodeAnalysis.CSharp.DeclarationTable.Cache.<>c__DisplayClass0.<_ctor>b__1()\r\n   at System.Lazy`1.CreateValue()\r\n   at System.Lazy`1.LazyInitValue()\r\n   at Microsoft.CodeAnalysis.CSharp.DeclarationTable.Cache.<_ctor>b__4()\r\n   at System.Lazy`1.CreateValue()\r\n   at System.Lazy`1.LazyInitValue()\r\n   at System.Lazy`1.get_Value()\r\n   at Microsoft.CodeAnalysis.CSharp.DeclarationTable.GetMergedReferenceDirectives()\r\n   at System.Lazy`1.CreateValue()\r\n   at System.Lazy`1.LazyInitValue()\r\n   at Microsoft.CodeAnalysis.CSharp.DeclarationTable.get_ReferenceDirectives()\r\n   at Microsoft.CodeAnalysis.CommonReferenceManager`2.GetCompilationReferences(TCompilation compilation, DiagnosticBag diagnostics, ImmutableArray`1& references, IDictionary`2& boundReferenceDirectives, ImmutableArray`1& referenceDirectiveLocations)\r\n   at Microsoft.CodeAnalysis.CommonReferenceManager`2.ResolveMetadataReferences(TCompilation compilation, ImmutableArray`1& references, IDictionary`2& boundReferenceDirectiveMap, ImmutableArray`1& boundReferenceDirectives, ImmutableArray`1& assemblies, ImmutableArray`1& modules, DiagnosticBag diagnostics)\r\n   at Microsoft.CodeAnalysis.CSharp.CSharpCompilation.ReferenceManager.CreateAndSetSourceAssemblyFullBind(CSharpCompilation compilation)\r\n   at Microsoft.CodeAnalysis.CSharp.CSharpCompilation.ReferenceManager.CreateSourceAssemblyForCompilation(CSharpCompilation compilation)\r\n   at Microsoft.CodeAnalysis.CSharp.CSharpCompilation.get_SourceAssembly()\r\n   at Microsoft.CodeAnalysis.CSharp.SyntaxTreeSemanticModel.GetDeclaredNamespace(NamespaceDeclarationSyntax declarationSyntax)\r\n   at Microsoft.CodeAnalysis.CSharp.SyntaxTreeSemanticModel.GetDeclaredNamespaceOrType(CSharpSyntaxNode declarationSyntax)\r\n   at Microsoft.CodeAnalysis.CSharp.SyntaxTreeSemanticModel.GetDeclaredTypeMemberContainer(CSharpSyntaxNode memberDeclaration)\r\n   at Microsoft.CodeAnalysis.CSharp.SyntaxTreeSemanticModel.GetDeclaredSymbol(BaseTypeDeclarationSyntax declarationSyntax, CancellationToken cancellationToken)\r\n   at Zbu.ModelsBuilder.Building.CodeParser.<>c__DisplayClass8.<Parse>b__0(ClassDeclarationSyntax x)\r\n   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()\r\n   at Zbu.ModelsBuilder.Building.CodeParser.Parse(ParseResult disco, CSharpCompilation compilation, SyntaxTree tree)\r\n   at Zbu.ModelsBuilder.Building.CodeParser.Parse(IDictionary`2 files, IEnumerable`1 referencedAssemblies)\r\n   at Zbu.ModelsBuilder.AspNet.ModelsBuilderApiController.GetModels(GetModelsData data)\r\n   at lambda_method(Closure , Object , Object[] )\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass13.<GetExecutor>b__c(Object instance, Object[] methodParameters)\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)\r\n   at System.Threading.Tasks.TaskHelpers.RunSynchronously[TResult](Func`1 func, CancellationToken cancellationToken)"}

ZbuModelsBuilder:    at Zbu.ModelsBuilder.AspNet.ModelsBuilderApi.EnsureSuccess(HttpResponseMessage result)

   at Zbu.ModelsBuilder.AspNet.ModelsBuilderApi.GetModels(Dictionary`2 ourFiles, String modelsNamespace)

   at Zbu.ModelsBuilder.CustomTool.CustomTool.ZbuModelsBuilder.GenerateRaw(String wszInputFilePath, String wszDefaultNamespace, IntPtr[] rgbOutputFileContents, UInt32& pcbOutput, String& errMsg)