diff --git a/src/Client/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/MainWindowViewModel.cs b/src/Client/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/MainWindowViewModel.cs
index fd28d36..c757bd6 100644
--- a/src/Client/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/MainWindowViewModel.cs
+++ b/src/Client/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/MainWindowViewModel.cs
@@ -252,7 +252,7 @@ public partial class MainWindowViewModel : ObservableObject
             }
 
             // Load root nodes
-            await BrowseTree.LoadRootsAsync();
+            if (BrowseTree != null) await BrowseTree.LoadRootsAsync();
 
             // Restore saved subscriptions
             if (_savedSubscribedNodes.Count > 0 && Subscriptions != null)
@@ -330,7 +330,7 @@ public partial class MainWindowViewModel : ObservableObject
         if (SelectedTreeNodes.Count == 0 || !IsConnected) return;
 
         var node = SelectedTreeNodes[0];
-        History.SelectedNodeId = node.NodeId;
+        if (History != null) History.SelectedNodeId = node.NodeId;
         SelectedTabIndex = 3; // History tab
     }