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.)>
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WinSCP 6.1.1

Error message:
Invalid access to memory.

Stack trace:
(00DFB3F4)
(00087AFF) ntdll.dll
(00073FD1) ntdll.dll.KiUserExceptionDispatcher
(00012004)
(00030518)
(00030662)
(0002BAA6)
(003F62DD)
(003B07EC)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.