<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 6.5.1

Error message:
Not enough timers available

Stack trace:
(0044D4D0) Vcl::Extctrls::TTimer::UpdateTimer
(0044D504) Vcl::Extctrls::TTimer::SetEnabled
(00528F1A) Driveview::TDriveView::CMRecreateWnd
(0039E286) Vcl::Controls::TControl::WndProc
(003A3431) Vcl::Controls::TWinControl::WndProc
(0040CB26) Vcl::Comctrls::TCustomTreeView::WndProc
(003A237E) Vcl::Controls::TWinControl::RecreateWnd
(003A3431) Vcl::Controls::TWinControl::WndProc

The problem happens rarely. I cannot reproduce it.