<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 5.10

Error message:
Error transferring file '/5345EA2DE76C646C/Pictures/Camera imports/2015-12-29/IMG_0310.JPG'.

Invalid access to memory.

Stack trace:
#000FC76C#
#0089950A# C5065_3
#0089B572# ____ExceptionHandler
#0089832C# __ExceptionHandler
#0008519F# ntdll.dll
#000731B1# ntdll.dll.KiUserExceptionDispatcher
#007BBC0B# TWebDAVFileSystem::SinkRobust
#007BE701# TWebDAVFileSystem::SinkFile
#0079CD5D# TTerminal::ProcessDirectory
#007BD347# TWebDAVFileSystem::Sink
#007BBC0B# TWebDAVFileSystem::SinkRobust
#007BE701# TWebDAVFileSystem::SinkFile
#0079CD5D# TTerminal::ProcessDirectory
#007BD347# TWebDAVFileSystem::Sink
#007BBC0B# TWebDAVFileSystem::SinkRobust
#007BB9FB# TWebDAVFileSystem::CopyToLocal
#007AD47A# TTerminal::CopyToLocal
#0000E3FD# TCustomScpExplorerForm::ExecuteFileOperation
#0000F0E4# TCustomScpExplorerForm::ExecuteFileOperation
#0001DE17# TCustomScpExplorerForm::RemoteFileControlFileOperation
#0001E174# TCustomScpExplorerForm::RemoteFileControlDDEnd
#0041A966# Customdirview::TCustomDirView::DDDragDetect
#0066B84E# TUnixDirView::DDDragDetect
#00416DF8# Customdirview::TCustomDirView::CNNotify
#00252F41# Vcl::Controls::TControl::WndProc
#00257A85# Vcl::Controls::TWinControl::WndProc
#0029B9B3# Vcl::Comctrls::TCustomListView::WndProc
#00257BEB# Vcl::Controls::_17076
#00257A85# Vcl::Controls::TWinControl::WndProc
#002570CC# Vcl::Controls::TWinControl::MainWndProc
#0037BA78# System::Classes::_18201
#00031B59# USER32.dll
#000240EE#

The problem happens rarely. I cannot reproduce it.