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 6.5

Error message:
Invalid access to memory.

Stack trace:
(00415CFC)
(00EF4C46)
(00EF6CBE)
(00EF3A68)
(000B046F) ntdll.dll
(0007AB0A) ntdll.dll.KiUserExceptionDispatcher
(005083BA)
(0051625D)
(000122A6)
(00012E88)
(00013104)
(000132C3)
(000514E1)
(00221688)

(00415CFC)
(000B046F) ntdll.dll
(0007AB0A) ntdll.dll.KiUserExceptionDispatcher
(005083BA)
(0051625D)
(000122A6)
(00012E88)
(00013104)
(000132C3)
(000514E1)
(00221688)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.