<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 6.3.3

Error message:
Invalid access to memory.

Stack trace:
(00E21DDA) __DynamicCastVCLptr
(00098CCF) ntdll.dll
(000781E1) ntdll.dll.KiUserExceptionDispatcher
(00CBA816) TFileFindDialog::Start
(00CBB0AB) TFileFindDialog::StartStopButtonClick
(00409495) Vcl::Controls::TWinControl::WndProc
(003716A4) Vcl::Stdctrls::TButtonControl::WndProc
(004095FB) Vcl::Controls::_17076
(00409495) Vcl::Controls::TWinControl::WndProc
(003C39A4) Vcl::Forms::TCustomForm::WndProc

The problem happens rarely. I cannot reproduce it.