<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 6.3.5

Error message:
Ошибка доступа к памяти.

Трассировка стека:
(00C57C4A) std::allocator<...
(00E24572) C6612_0
(00E265DA) ____ExceptionHandler
(00E23394) __ExceptionHandler
(0005A466) ntdll.dll
(0000F12E) ntdll.dll.KiUserExceptionDispatcher
(00C57A8D) TParallelOperation::TParallelOperation
(00B7D280) TTransferQueueItem::DoExecute
(00B7C5CE) TQueueItem::Execute
(00B7B5FE) TTerminalItem::ProcessEvent
(00B79934) TSignalThread::Execute
(000D246B) Userinterface::C20_0
(00012368) kernel32.dll.BaseThreadInitThunk
(00038F70) ntdll.dll
(00038F40) ntdll.dll

The problem happens rarely. I cannot reproduce it.