diff --git a/VisualPascalABCNET/FileMonitoring.cs b/VisualPascalABCNET/FileMonitoring.cs
index b61b04b48..eaa993ddd 100644
--- a/VisualPascalABCNET/FileMonitoring.cs
+++ b/VisualPascalABCNET/FileMonitoring.cs
@@ -90,17 +90,18 @@ namespace VisualPascalABC
 
         void MainForm_Activated(object sender, EventArgs e) => System.Threading.Tasks.Task.Run(() =>
         {
+            if (!wasChangedExternally) return;
+            wasChangedExternally = false;
             try
             {
-                if (wasChangedExternally)
+                string mes = null;
+                if (!File.Exists(fileName))
                 {
-                    wasChangedExternally = false;
-
-                    string mes = null;
-                    if (!File.Exists(fileName))
+                    mes = Form1StringResources.Get("FILE_NOT_EXIST_MESSAGE");
+                    var dr = MessageBox.Show(fileName + "\n\n" + mes, Form1StringResources.Get("CHANGED_FILE"), MessageBoxButtons.YesNo, MessageBoxIcon.Question);
+                    VisualPABCSingleton.MainForm.Invoke((Action)(() =>
                     {
-                        mes = Form1StringResources.Get("FILE_NOT_EXIST_MESSAGE");
-                        if (MessageBox.Show(fileName + "\n\n" + mes, Form1StringResources.Get("CHANGED_FILE"), MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
+                        if (dr == DialogResult.Yes)
                         {
                             WorkbenchServiceFactory.FileService.SetFileAsChanged(fileName);
                         }
@@ -108,24 +109,27 @@ namespace VisualPascalABC
                         {
                             WorkbenchServiceFactory.FileService.CloseFile(fileName);
                         }
-                        return;
-                    }
-
-                    mes = Form1StringResources.Get("FILE_CHANGED_MESSAGE");
-                    if (MessageBox.Show(fileName + "\n\n" + mes, Form1StringResources.Get("CHANGED_FILE"), MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
-                    {
-                        WorkbenchServiceFactory.FileService.ReloadFile(fileName);
-                    }
-                    else
-                    {
-                        WorkbenchServiceFactory.FileService.SetFileAsChanged(fileName);
-                    }
+                    }));
+                }
+                else
+                {
+                    mes = Form1StringResources.Get("FILE_CHANGED_MESSAGE");
+                    var dr = MessageBox.Show(fileName + "\n\n" + mes, Form1StringResources.Get("CHANGED_FILE"), MessageBoxButtons.YesNo, MessageBoxIcon.Question);
+                    VisualPABCSingleton.MainForm.Invoke((Action)(() =>
+                    {
+                        if (dr == DialogResult.Yes)
+                        {
+                            WorkbenchServiceFactory.FileService.ReloadFile(fileName);
+                        }
+                        else
+                        {
+                            WorkbenchServiceFactory.FileService.SetFileAsChanged(fileName);
+                        }
+                    }));
                 }
-            }
-            catch (Exception)
-            {
 
             }
+            catch (Exception) {}
         });
 
     }