SourceTree 2.3.1 crashes at startup

SourceTree crashes on start.

I uninstalled and cleaned %APPDATA% folder.

I installed SRCTREE from scratch but the problem remains.

I found a sourcetree.log file with the following information:

ERROR [2017-10-27 11:26:42,810] [1] [SourceTree.App] [.ctor] - finish EnsureSquirrelExecutionStubIsCopied
ERROR [2017-10-27 11:26:42,986] [1] [SourceTree.App] [OnStartup] - Failed to start
System.NullReferenceException: Object reference not set to an instance of an object.
{{ at SourceTree.Notifications.NotificationsManager.SetOwner(NotificationDialogWindow notificationWindow)}}
{{ at SourceTree.Notifications.NotificationsManager.ShowNotificationDialog[T](NotificationDialogWindow notificationWindow, Tuple`2 customAction, VistaTaskDialogIcon icon)}}
{{ at SourceTree.Notifications.NotificationsManager.ShowNotificationDialog[T](String title, String message, Tuple`2 customAction, String cancelLabel, String suppressionSetting, Action`1 suppressionChangedAction, Object contentControl, String contentCommandLabel, Action contentAction)}}
{{ at SourceTree.Notifications.NotificationsManager.ShowNotificationDialogWithYesConfirmation(String title, String message, String details)}}
{{ at SourceTree.Configuration.WpfSpellCheckerPreFlightCheck.Run()}}
{{ at SourceTree.AppRoot.RunPreFlightChecks()}}
{{ at SourceTree.AppRoot.OnStartup(StartupEventArgs e)}}
{{ at SourceTree.App.OnStartup(StartupEventArgs e)}}