<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 6.5.6

Error message:
Invalid access to memory.

Stack trace:
(107FF3E9)WinSCP.exe
(0008822F) ntdll.dll
(00074711) ntdll.dll.KiUserExceptionDispatcher
(00221920) System::Actions::TContainedActionList::UpdateAction
(0038ADA1) Vcl::Actnlist::TCustomAction::Update
(004ACF22) Vcl::Forms::_16859
(004ACF22) Vcl::Forms::_16859
(004ACF93) Vcl::Forms::TCustomForm::UpdateActions
(0000A47D) TCustomScpExplorerForm::UpdateActions
(0002D5A0) TCustomScpExplorerForm::Dispatch
(0039E3C2) Vcl::Controls::TControl::WndProc
(003A356D) Vcl::Controls::TWinControl::WndProc
(004A77B4) Vcl::Forms::TCustomForm::WndProc
(00E0720C) Vclcommon::C4884_0
(00E073CE) Vclcommon::C4884_0
(0039DFF8) Vcl::Controls::TControl::Perform
(003A2819) Vcl::Controls::TWinControl::UpdateShowing
(003A292E) Vcl::Controls::TWinControl::UpdateControlState
(003A56F2) Vcl::Controls::TWinControl::CMVisibleChanged
(0039E3C2) Vcl::Controls::TControl::WndProc
(003A356D) Vcl::Controls::TWinControl::WndProc
(004A77B4) Vcl::Forms::TCustomForm::WndProc
(00E07493) Vclcommon::C4884_0
(0039DFF8) Vcl::Controls::TControl::Perform
(0039CA26) Vcl::Controls::TControl::SetVisible
(0012A249) Execute
(000033BB) wWinMain
(00EF5641) C7146_0
(000672AC) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00067279) ntdll.dll.RtlGetAppContainerNamedObjectPath

(107FF3E9)WinSCP.exe
(00EF78FE)
(00EF9976)
(00EF6720) __ExceptionHandler
(0008822F) ntdll.dll
(00074711) ntdll.dll.KiUserExceptionDispatcher
(00221920) System::Actions::TContainedActionList::UpdateAction
(0038ADA1) Vcl::Actnlist::TCustomAction::Update
(004ACF22) Vcl::Forms::_16859
(004ACF22) Vcl::Forms::_16859
(004ACF93) Vcl::Forms::TCustomForm::UpdateActions
(0000A47D) TCustomScpExplorerForm::UpdateActions
(0002D5A0) TCustomScpExplorerForm::Dispatch
(0039E3C2) Vcl::Controls::TControl::WndProc
(003A356D) Vcl::Controls::TWinControl::WndProc
(004A77B4) Vcl::Forms::TCustomForm::WndProc
(00E0720C) Vclcommon::C4884_0
(00E073CE) Vclcommon::C4884_0
(0039DFF8) Vcl::Controls::TControl::Perform
(003A2819) Vcl::Controls::TWinControl::UpdateShowing
(003A292E) Vcl::Controls::TWinControl::UpdateControlState
(003A56F2) Vcl::Controls::TWinControl::CMVisibleChanged
(0039E3C2) Vcl::Controls::TControl::WndProc
(003A356D) Vcl::Controls::TWinControl::WndProc
(004A77B4) Vcl::Forms::TCustomForm::WndProc
(00E07493) Vclcommon::C4884_0
(0039DFF8) Vcl::Controls::TControl::Perform
(0039CA26) Vcl::Controls::TControl::SetVisible
(0012A249) Execute
(000033BB) wWinMain
(00EF5641) C7146_0
(000672AC) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00067279) ntdll.dll.RtlGetAppContainerNamedObjectPath

The problem happens rarely. I cannot reproduce it.