vSphere Client Startup Error: System.Reflection.TargetInvocationException

I get this error when starting up vSpere Client 5.1.0:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Net.Sockets.SocketException: The requested name is valid, but no data of the requested type was found
   at System.Net.Dns.GetAddrInfo(String name)
   at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at VpxClient.Toolbars.VirtualMachineToolbar..ctor()
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle._InvokeConstructor(Object[] args, SignatureStruct& signature, IntPtr declaringType)
   at System.RuntimeMethodHandle.InvokeConstructor(Object[] args, SignatureStruct signature, RuntimeTypeHandle declaringType)
   at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at VpxClient.Common.ComponentLoader.GetToolBar(ManagedObject mo)
   at VpxClient.Common.ComponentLoader.GetComponent[T](String componentId, ManagedObject mo)
   at VpxClient.Toolbars.InventoryToolbarContainer.CreateOrRecycleToolbarFor(Types managedObjectType, ManagedObjectArray moArray)
   at VpxClient.Toolbars.InventoryToolbarContainer.AddToolbarsFor(ManagedObjectArray selectedMOs, Object sender, String sToolbarProp)
   at VpxClient.Toolbars.InventoryToolbarContainer.SelectionChanged(Object sender)
   at VpxClient.InventoryView.SelectionChanged(Object sender)
   at VpxClientCommon.SelectionChangedEventHandler.Invoke(VimNavView sender)
   at VpxClientCommon.NavView.OnSelectionChanged()
   at VpxClientCommon.NavView.tree_AfterSelect(Object sender, TreeViewEventArgs e)
   at System.Windows.Forms.TreeView.OnAfterSelect(TreeViewEventArgs e)
   at VMware.CustomControls.TreeViewEx.OnAfterSelect(TreeViewEventArgs e)
   at System.Windows.Forms.TreeView.TvnSelected(NMTREEVIEW* nmtv)
   at System.Windows.Forms.TreeView.WmNotify(Message& m)
   at System.Windows.Forms.TreeView.WndProc(Message& m)
   at VMware.CustomControls.TreeViewEx.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)