I get the same problem. I downloaded the windows client msi on 7/Jun/2011 ~2am GMT. Windows gives me the option to debug as I have visual studio installed. I'm able to replicate this bug fairly reliably too. Hopes this helps Mandel. Let me know if you want me to grab anything else. Cheers Jered System.InvalidOperationException was unhandled Message=Cannot set Visibility or call Show, ShowDialog, or WindowInteropHelper.EnsureHandle after a Window has closed. Source=PresentationFramework StackTrace: at System.Windows.Window.ShowDialog() at Canonical.UbuntuOne.Client.Views.PreferencesDialog.Canonical.UbuntuOne.Client.Preferences.IPreferencesView.ShowDialog() in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\Canonical.UbuntuOne.Client.Views\PreferencesDialog.xaml.cs:line 176 at Canonical.UbuntuOne.Client.Preferences.PreferencesDialogPresenter.Show() in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\Canonical.UbuntuOne.Client\Preferences\PreferencesDialogPresenter.cs:line 212 at Canonical.UbuntuOne.Client.Notification.NotificationIconPresenter.OpenUbuntuOnePreferences() in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\Canonical.UbuntuOne.Client\Notification\NotificationIconPresenter.cs:line 326 at Canonical.UbuntuOne.Client.Views.UbuntuOneNotifyIcon.OnUbuntuOnePreferencesMenuItemClick(Object sender, RoutedEventArgs e) in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\Canonical.UbuntuOne.Client.Views\NotifyIcon.xaml.cs:line 219 at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args) at System.Windows.Controls.MenuItem.InvokeClickAfterRender(Object arg) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Threading.DispatcherOperation.Invoke() at System.Windows.Threading.Dispatcher.ProcessQueue() at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Application.RunInternal(Window window) at Canonical.UbuntuOne.Common.Utils.ApplicationWrapper.Run(Window startWindow) in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\Canonical.UbuntuOne.Common\Utils\ApplicationWrapper.cs:line 67 at UbuntuOneClient.Program.StartApplication() in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\UbuntuOneClient\Program.cs:line 134 at UbuntuOneClient.Program.Main() in c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\UbuntuOneClient\Program.cs:line 163 InnerException: --- c:\Users\Mandel\Documents\Projects\ubuntuone\net\chipaca_trunk\src\UbuntuOneClient\Program.cs 00000000 sub rsp,58h 00000004 mov qword ptr [rsp+20h],0 0000000d mov rax,7FF000134D8h 00000017 mov eax,dword ptr [rax] 00000019 test eax,eax 0000001b je 0000000000000022 0000001d call FFFFFFFFE9386D70 00000022 nop 00000023 mov rcx,12782FD0h 0000002d mov rcx,qword ptr [rcx] 00000030 mov rdx,127832F8h 0000003a mov rdx,qword ptr [rdx] 0000003d lea rax,[FFEEB650h] 00000044 mov qword ptr [rsp+28h],rax 00000049 mov qword ptr [rsp+30h],rcx 0000004e mov rax,qword ptr [rsp+30h] 00000053 cmp byte ptr [rax],0 00000056 mov rcx,qword ptr [rsp+30h] 0000005b mov r11,qword ptr [rsp+28h] 00000060 mov rax,qword ptr [rsp+28h] 00000065 call qword ptr [rax] 00000067 nop 00000068 lea rcx,[00052F48h] 0000006f call FFFFFFFFE8FE9B20 00000074 mov qword ptr [rsp+38h],rax 00000079 mov rax,qword ptr [rsp+38h] 0000007e mov qword ptr [rsp+40h],rax 00000083 mov rcx,qword ptr [rsp+40h] 00000088 call FFFFFFFFFFEE99F0 0000008d mov rcx,qword ptr [rsp+40h] 00000092 call FFFFFFFFFFEE9AA8 00000097 nop 00000098 lea rcx,[00053258h] 0000009f call FFFFFFFFFFEE9B10 000000a4 mov qword ptr [rsp+48h],rax 000000a9 mov rax,qword ptr [rsp+48h] 000000ae mov qword ptr [rsp+20h],rax 000000b3 mov rax,qword ptr [rsp+20h] 000000b8 cmp byte ptr [rax],0 000000bb mov rcx,qword ptr [rsp+20h] 000000c0 call FFFFFFFFFFEE75D8 000000c5 nop //BREAKS HERE 000000c6 jmp 00000000000000C8 000000c8 add rsp,58h 000000cc ret