title: Error when trying to view the Application Properties page in Visual Studio 2017
body: <p>When trying to open the Properties of a WPF application, on the Application page, it gives the following error: </p>
  
  <blockquote>
    <p>An error occurred trying to load the page. The method or operation is not implemented.</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/wX0uB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wX0uB.png" alt="screenshot"></a></p>
  
  <p>In the Windows Event Viewer I  can find this:</p>
  
  <pre class="lang-none prettyprint-override"><code>Error Information 
  AppInsightsEvent Name = vs/ml/proppages/appdesigner/prop-page-designer-view-fault
  Description           = ActivatePage
  TelemetrySession      = '4a288b83-00d2-4f45-84cf-513352811580' Started = True OptIn=True IsInitialized = True Cloned = False
  WatsonEventType       = VisualStudioNonFatalErrors2
  UTC time              = 2019-03-07T10:27:40
  
  Exception:  System.NotImplementedException  
  The method or operation is not implemented. 
  
  Microsoft.VisualStudio.Editors.PropertyPages.WPF.ApplicationPropPageVBWPF.StartupObjectOrUri.GetHashCode()
  System.Collections.Hashtable.GetHash(Object key) 
  System.Collections.Hashtable.InitHash(Object key, Int32 hashsize, UInt32&amp; seed, UInt32&amp; incr) 
  System.Collections.Hashtable.ContainsKey(Object key) 
  System.Windows.Forms.ComboBox.ComboBoxItemAccessibleObjectCollection.get_Item(Object key) 
  System.Windows.Forms.ComboBox.ComboBoxUiaProvider.SetComboBoxItemSelection()
  System.Windows.Forms.ComboBox.OnSelectedIndexChanged(EventArgs e) 
  System.Windows.Forms.ComboBox.set_SelectedIndex(Int32 value) 
  System.Windows.Forms.ComboBox.set_SelectedItem(Object value) 
  Microsoft.VisualStudio.Editors.PropertyPages.WPF.ApplicationPropPageVBWPF.SetSelectedStartupObjectOrUriIntoCombobox(ComboBox combobox, StartupObjectOrUri startupObjectOrUri) 
  Microsoft.VisualStudio.Editors.PropertyPages.WPF.ApplicationPropPageVBWPF.SetStartupObjectOrUriIntoUI(Control control, PropertyDescriptor prop, Object value) 
  Microsoft.VisualStudio.Editors.PropertyPages.PropertyControlData.InitPropertyUI()
  Microsoft.VisualStudio.Editors.PropertyPages.PropPageUserControlBase.InitPage()
  Microsoft.VisualStudio.Editors.PropertyPages.PropPageUserControlBase.SetObjects(Object[] objects) 
  Microsoft.VisualStudio.Editors.PropertyPages.PropPageUserControlBase.IPropertyPageInternal_SetObjects(Object[] objects) 
  Microsoft.VisualStudio.Editors.PropertyPages.PropPageBase.Create(IntPtr hWndParent) 
  Microsoft.VisualStudio.Editors.PropertyPages.PropPageBase.IPropertyPage2_Activate(IntPtr hWndParent, RECT[] pRect, Int32 bModal) 
  Microsoft.VisualStudio.Editors.PropPageDesigner.PropPageDesignerView.ActivatePage(IPropertyPage PropPage)
  </code></pre>
  
  <h2>What I've Tried</h2>
  
  <ul>
  <li>I previously installed the Visual Studio 2019 RC, but have now uninstalled it. That version also gave the same error.  </li>
  <li>Reinstalling Visual Studio 2017 didn't help.</li>
  <li>This happens in old and freshly created projects.</li>
  <li>My coworker doesn't have this on his computer with the same projects.</li>
  <li>I did not have any problems last week. I haven't installed/uninstalled anything special.</li>
  </ul>