(00215A2D) System::Classes::_17621 - System::Classes::TStream::WriteDescendent

<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 6.3.7

Error message:
(00215A2D) System::Classes::_17621
(00212176) System::Classes::TStream::WriteDescendent
(00207BBB) __tpdsc__ System::TArray__1<System::Generics::Collections::TList__1<System::Classes::TComponent *> *>
(0020950F) System::Classes::InitInheritedComponent
(0020959D) System::Classes::InitInheritedComponent
(003C1E0E) Vcl::Forms::TCustomForm::TCustomForm
(00005912) Vcl::Forms::TForm::TForm
(00CBB8FE) TFileFindDialog::FormShow
(00CBB7E6) TFileFindDialog::FormShow
(0002ED33) TCustomScpExplorerForm::SessionsPageControlMouseDown
(0004FD45) TNonVisualDataModule::ExplorerActionsExecute
(0027581C) System::Actions::TContainedActionList::UpdateAction
(003595FD) Vcl::Actnlist::TCustomAction::GetImages
(00226F7C) System::Classes::MakeObjectInstance
(00040829) USER32.dll
(00036F15) USER32.dll
(000357BB) USER32.dll
(000352EB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.