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 6.1.1

Error message:
Invalid access to memory.

Stack trace:
(003F90F7)
(0009812F) ntdll.dll
(00077D31) ntdll.dll.KiUserExceptionDispatcher
(004802D9)
(004802D9)
(00480368)
(00492ADE)
(0047FFF9)
(003CCDAF)
(00214D98)
(00031E61) USER32.dll
(00022C41) USER32.dll
(00021500) USER32.dll
(0002104B) USER32.dll.DispatchMessageW

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.