<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 6.3.2

Error message:
Invalid access to memory.

Stack trace:
(002A73EB) System::DoneExcept
(00087B9F) ntdll.dll
(00074121) ntdll.dll.KiUserExceptionDispatcher
(00226F88) System::Classes::_18201
(00040999) USER32.dll
(00036DB5) USER32.dll
(000356EC) USER32.dll
(0003520B) USER32.dll.DispatchMessageW

(002A6FD8) System::HandleAnyException
(00087B9F) ntdll.dll
(00074121) ntdll.dll.KiUserExceptionDispatcher
(00226F88) System::Classes::_18201
(00040999) USER32.dll
(00036DB5) USER32.dll
(000356EC) USER32.dll
(0003520B) USER32.dll.DispatchMessageW

Status: all_insignificant

The problem happens rarely. I cannot reproduce it.