<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 6.5.3

Error message:
Invalid access to memory.

Stack trace:
(1B1A0918)WinSCP.exe
(000B32FF) ntdll.dll
(0007A66A) ntdll.dll.KiUserExceptionDispatcher
(0009E720) TScreenTipHintWindow::UseBoldShortHint
(003A9AE7) Vcl::Controls::TCustomControl::PaintWindow
(003A3615) Vcl::Controls::TWinControl::PaintHandler
(003A3E10) Vcl::Controls::TWinControl::WMPaint
(003A9A81) Vcl::Controls::TCustomControl::WMPaint
(003A3455) Vcl::Controls::TWinControl::WndProc
(003A2960) Vcl::Controls::TWinControl::MainWndProc
(00204B78) System::Classes::_18364
(00038B11) USER32.dll
(00026C58) USER32.dll
(000266FB) USER32.dll
(00032F87) USER32.dll
(0007A644) ntdll.dll.KiUserCallbackDispatcher
(00025C4B) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.