In the connection window i made a right klick on a folder and selected to delete the folder with it content. After confirming the message that it is going to be deleted WinSCP showed the error message.

WinSCP 5.7.6

Error message:
Invalid access to memory.

Stack trace:
(007E802B)
(0007C53F) ntdll.dll
(00069D7A) ntdll.dll.KiUserExceptionDispatcher
(007E841D)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.