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.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.3.6

Error message:
Invalid access to memory.

Stack trace:
(0043A8A3)
(00095A5F) ntdll.dll
(00075441) ntdll.dll.KiUserExceptionDispatcher
(00493094)
(004A593A)
(00492D25)
(003DFB4B)
(00226F74)
(00046801) USER32.dll
(00026FB5) USER32.dll
(00025AB0) USER32.dll
(000255DB) USER32.dll.DispatchMessageW

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.