<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 6.3.6

Error message:
Invalid access to memory.

Stack trace:
(002A7367) System::DoneExcept
(0008818F) ntdll.dll
(00074711) ntdll.dll.KiUserExceptionDispatcher
(00226F74) System::Classes::_18201
(00040489) USER32.dll
(00036B75) USER32.dll
(0003541B) USER32.dll
(00034F4B) USER32.dll.DispatchMessageW

(002A6F54) System::HandleAnyException
(0008818F) ntdll.dll
(00074711) ntdll.dll.KiUserExceptionDispatcher
(00226F74) System::Classes::_18201
(00040489) USER32.dll
(00036B75) USER32.dll
(0003541B) USER32.dll
(00034F4B) USER32.dll.DispatchMessageW

Status: all_insignificant

The problem happens rarely. I cannot reproduce it.