diff --git a/ModelManager.cs b/ModelManager.cs
index d1ef915..d73547e 100644
--- a/ModelManager.cs
+++ b/ModelManager.cs
@@ -133,6 +133,12 @@ public string LoadModel(string filePath, string repositoryPath, string baseWebUr
                     {
                         foreach (var jj in ii.RequiredModel)
                         {
+                            if (nodeset.Models.FirstOrDefault(m => m.ModelUri == jj.ModelUri) != null)
+                            {
+                                // RequiredModel is defined in the current document. Will be created later.
+                                continue;
+                            }
+
                             if (jj.ModelUri == Opc.Ua.Namespaces.OpcUa)
                             {
                                 hasCoreModel = true;
diff --git a/NodeSetToAML.cs b/NodeSetToAML.cs
index 39ed46f..b8b957e 100644
--- a/NodeSetToAML.cs
+++ b/NodeSetToAML.cs
@@ -741,7 +741,10 @@ private AttributeType AddModifyAttribute(AttributeSequence seq, string name, str
                 desiredAttribute = seq.Append(name);  // not found so create a new one
             }
 
-            RecreateAttributeInstance(sourceAttribute, desiredAttribute);
+            if (sourceAttribute != null)
+            {
+                RecreateAttributeInstance(sourceAttribute, desiredAttribute);
+            }
 
             if (val.TypeInfo != null)
             {
@@ -832,6 +835,12 @@ private AttributeType AddModifyAttribute(AttributeSequence seq, string name, str
                                         {
                                             Variant elementVariant = new Variant(valueAsList[index]);
                                             ExtensionObject extensionObject = elementVariant.Value as ExtensionObject;
+
+                                            if (extensionObject.Encoding == ExtensionObjectEncoding.None)
+                                            {
+                                                continue;
+                                            }
+
                                             NodeId typeId = ExpandedNodeId.ToNodeId(extensionObject.TypeId, m_modelManager.NamespaceUris);
 
                                             Type extentionObjectType = extensionObject.Body.GetType();
@@ -2734,6 +2743,10 @@ private void AddNonHierarchicalReferences()
                 UANode targetNode = m_modelManager.FindNode<UANode>(referenceHolder.Reference.TargetId);
                 SystemUnitClassType targetSystemUnitClass = FindNonHierarchicalReference(referenceHolder,
                     targetNode);
+                if (targetSystemUnitClass == null)
+                {
+                    continue;
+                }
                 string targetPath = GetCreatedPathName(targetNode);
 
                 string refURI = m_modelManager.FindModelUri(referenceHolder.Reference.ReferenceTypeId);
@@ -2743,8 +2756,8 @@ private void AddNonHierarchicalReferences()
                     referenceTypeNode.DecodedBrowseName.Name,
                     sourceSystemUnitClass.Name,
                     sourceSystemUnitClass.ID,
-                    targetSystemUnitClass.Name,
-                    targetSystemUnitClass.ID);
+                    targetSystemUnitClass?.Name,
+                    targetSystemUnitClass?.ID);
 
                 ExternalInterfaceType sourceInterface = FindOrAddSourceInterface(ref sourceSystemUnitClass,
                     refURI, 
diff --git a/OrderModelInfo.cs b/OrderModelInfo.cs
index 90a6ccf..7e973d9 100644
--- a/OrderModelInfo.cs
+++ b/OrderModelInfo.cs
@@ -67,7 +67,7 @@ public List<ModelInfo> GetProcessOrder( List<ModelInfo> initial )
         public void AddCompiled( string uri, HashSet<string> set,
             Dictionary<string, ModelInfo> source )
         {
-            if( source.TryGetValue( uri, out ModelInfo modelInfo ) )
+            if( source.TryGetValue( uri, out ModelInfo modelInfo ) && !set.Contains(uri))
             {
                 if ( modelInfo.NodeSet != null && 
                     modelInfo.NodeSet.Models != null )