System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object
  at (wrapper stelemref) System.Object:stelemref (object,intptr,object)
  at System.Collections.ArrayList.Add (System.Object value) [0x00000] 
  at Gtk.VBox..ctor (Boolean homogeneous, Int32 spacing) [0x00000] 
  at Gtk.VBox..ctor () [0x00000] 
  at MonoDevelop.Core.Gui.Components.FileBrowser..ctor () [0x00000] 
  at MonoDevelop.Ide.Gui.Pads.FileScout..ctor () [0x00000] 
  at <0x00000> <unknown method>
  at (wrapper managed-to-native) System.Reflection.MonoCMethod:InternalInvoke (object,object[])
  at System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] --- End of inner exception stack trace ---

  at System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  at System.Reflection.MonoCMethod.Invoke (BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  at System.Reflection.ConstructorInfo.Invoke (System.Object[] parameters) [0x00000] 
  at System.Activator.CreateInstance (System.Type type, Boolean nonPublic) [0x00000] 
  at System.Activator.CreateInstance (System.Type type) [0x00000] 
  at MonoDevelop.Core.AddIns.AddIn.CreateObject (System.String className) [0x00000] 
  at MonoDevelop.Ide.Codons.PadCodon.CreatePad () [0x00000] 
  at MonoDevelop.Ide.Codons.PadCodon.BuildItem (System.Object owner, System.Collections.ArrayList subItems, MonoDevelop.Core.AddIns.ConditionCollection conditions) [0x00000] 
  at MonoDevelop.Core.AddIns.DefaultAddInTreeNode.BuildChildItems (System.Object caller) [0x00000] 
  at MonoDevelop.Core.AddIns.AddInService.GetTreeItems (System.String path, System.Type itemType) [0x00000] 
  at MonoDevelop.Ide.Gui.DefaultWorkbench.InitializeLayout (IWorkbenchLayout workbenchLayout) [0x00000] 
  at MonoDevelop.Ide.Gui.Workbench.Initialize (IProgressMonitor monitor) [0x00000] 
  at MonoDevelop.Ide.Gui.IdeApp.Initialize (IProgressMonitor monitor) [0x00000] 
  at MonoDevelop.Ide.Gui.IdeStartup.Run (System.String[] args) [0x00000]