Invalid access to memory

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
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WinSCP 6.3.3

Error message:
Invalid access to memory.

Stack trace:
(002A761F) System::DoneExcept
(00098CCF) ntdll.dll
(000781E1) ntdll.dll.KiUserExceptionDispatcher
(002271BC) System::Classes::_18201
(00032771) USER32.dll
(00023591) USER32.dll
(00021E50) USER32.dll
(0002199B) USER32.dll.DispatchMessageW

(002A720C) System::HandleAnyException
(00098CCF) ntdll.dll
(000781E1) ntdll.dll.KiUserExceptionDispatcher
(002271BC) System::Classes::_18201
(00032771) USER32.dll
(00023591) USER32.dll
(00021E50) USER32.dll
(0002199B) USER32.dll.DispatchMessageW

Status: all_insignificant

The problem happens rarely. I cannot reproduce it.