Going through the Event Viewer I found this:

Application: TestApplication.exe Framework Version: v4.0.30319 Description: The process was terminated due to an unhandled exception. Exception Info: System.IndexOutOfRangeException at Telerik.WinControls.UI.RadPopupContainerForm.OnKeyDown(System.Windows.Forms.Keys) at Telerik.WinControls.UI.PopupManager.OnKeyDown(System.Windows.Forms.Message ByRef) at Telerik.WinControls.UI.PopupManager.Telerik.WinControls.IMessageListener.PreviewMessage(System.Windows.Forms.Message ByRef) at Telerik.WinControls.RadMessageFilter.NotifyGetMessageEvent(System.Windows.Forms.Message ByRef) at Telerik.WinControls.RadMessageFilter.GetMessageHookProc(Int32, IntPtr, IntPtr)