<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.3.3

Error message:
External exception C0000258

Stack trace:
(0007AB78) ntdll.dll.KiUserCallbackDispatcher
(000B03FF) ntdll.dll
(0007AB8A) ntdll.dll.KiUserExceptionDispatcher
(0003CE73) USER32.dll
(000242F1) USER32.dll.SendMessageW
(0043AED7) Vcl::Comctrls::TTreeNode::GetState
(00AE9143) TUnixDirView::SaveState
(00022D5D) TCustomScpExplorerForm::UpdateSession
(000591EF) TScpCommanderForm::UpdateSession
(000C2679) TTerminalManager::ReconnectActiveTerminal
(000D3A68) ShowExtendedExceptionEx
(00025DA8) TCustomScpExplorerForm::ShowExtendedException
(000C3E41) TTerminalManager::TerminalShowExtendedException
(00C6137C) TTerminal::ShowExtendedException
(000C2693) TTerminalManager::ReconnectActiveTerminal
(000D3A68) ShowExtendedExceptionEx
(00025DA8) TCustomScpExplorerForm::ShowExtendedException
(000C3E41) TTerminalManager::TerminalShowExtendedException
(00C6137C) TTerminal::ShowExtendedException
(003CD426) Vcl::Forms::TApplication::HandleException
(002271BC) System::Classes::_18201
(00036461) USER32.dll
(00024B28) USER32.dll
(00023FB5) USER32.dll
(00023B1B) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.