<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)>
Was attempting to syncronize 2 different Network Attached Storage Drives.
WinSCP 6.7.1

Error message:
Invalid access to memory.

Stack trace:
(0002EBFD) TCustomScpExplorerForm::SynchronizeApplyLocal
(000B51E0) ntdll.dll
(000B51AF) ntdll.dll
(0006CC4E) ntdll.dll
(0007962A) ntdll.dll
(00169726) windows.storage.dll
(001D4759) windows.storage.dll
(001D4724) windows.storage.dll
(0002EBDB) TCustomScpExplorerForm::SynchronizeApplyLocal
(0015C5FF) KERNELBASE.dll
(0002F1FF) TCustomScpExplorerForm::FullSynchronize
(00232F8A) System::Classes::TComponent::RemoveNotification
(0055B01B) Dragdrop::TDragDrop::Notification
(001B3CFE) System::Generics::Collections::TListHelper::DoRemoveFwd4
(00232F8A) System::Classes::TComponent::RemoveNotification
(001B3CFE) System::Generics::Collections::TListHelper::DoRemoveFwd4
(00232FCF) System::Classes::TComponent::RemoveFreeNotification
(001B4C48) System::Generics::Collections::TListHelper::InternalDoDelete4
(001B3D0F) System::Generics::Collections::TListHelper::DoRemoveFwd4
(00232CEE) System::Classes::TComponent::Remove
(0016AA26) System::UTF8IdentToString
(0016B710) System::TMonitor::Enter
(00226C66) System::Classes::RemoveFixups
(00061643) ntdll.dll
(0015C773) KERNELBASE.dll
(0015C7C2) KERNELBASE.dll
(0015C5FF) KERNELBASE.dll
(0018D383) System::Sysutils::TryEncodeTime
(00032E02) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(00027A63) USER32.dll
(00027E79) USER32.dll
(0002CE19) USER32.dll
(00038CC1) USER32.dll
(00027A63) USER32.dll
(00027E79) USER32.dll
(0002CF03) USER32.dll
(0002D8D5) USER32.dll
(0002781B) USER32.dll
(000329D7) USER32.dll
(0007727A) ntdll.dll
(000329EB) USER32.dll
(0016CCA5) System::UStrFromPWCharLen
(0016DDF4) System::UStrCopy
(0053D2CE) Dirviewint::TDirViewInt::GetPath
(000696C5) TScpCommanderForm::FullSynchronizeDirectories
(00446EE6) Vcl::Comctrls::TCustomListView::IsEditing
(000628B6) TNonVisualDataModule::GetBusy
(0005B97E) TNonVisualDataModule::ExplorerActionsExecute
(003CA312) Vcl::Controls::TControl::WndProc
(0002781B) USER32.dll
(003CF4BD) Vcl::Controls::TWinControl::WndProc
(0016BBE8) System::TMonitor::TryEnter
(00052344) TNonVisualDataModule::ExplorerActionsUpdate
(003AFE15) Vcl::Graphics::FreeMemoryContexts
(003CE9C8) Vcl::Controls::TWinControl::MainWndProc
(003CE9DD) Vcl::Controls::TWinControl::MainWndProc
(003CEC7C) Vcl::Controls::TWinControl::IsControlMouseMsg
(00251F14) System::Actions::TContainedActionList::ExecuteAction
(0016B0E2) System::CallDynaInst
(003B6A21) Vcl::Actnlist::TCustomAction::Execute
(00234357) System::Classes::TBasicActionLink::Execute
(005769F0) Tb2item::TTBCustomItem::Click
(005768E3) Tb2item::TTBCustomItem::ClickWndProc
(0023533C) System::Classes::_18364
(00038CC1) USER32.dll
(00027D78) USER32.dll
(00027A63) USER32.dll
(0007727A) ntdll.dll
(0003334E) USER32.dll
(00026D45) USER32.dll
(000268AB) USER32.dll
(004DDA2F) Vcl::Forms::TApplication::ProcessMessage
(004DDA72) Vcl::Forms::TApplicati

The problem happens rarely. I cannot reproduce it.

@jmichaelmeehan: Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.

Doing a synchronize between two sets of directories on two local external USB drives.
No network remote access involved.
Task manage shows memory usage as 19.3 MB

<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 6.7

Error message:
Invalid access to memory.

Stack trace:
(0002F151) TCustomScpExplorerForm::SynchronizeApplyLocal
(00088350) ntdll.dll
(0008831F) ntdll.dll
(000689DA) ntdll.dll
(000747C1) ntdll.dll
(009BEF59) std::_Tree<std::_Tmap_traits<System::UnicodeString, TSynchronizeChecklist::TItem *, std::less<System::UnicodeString>, std::allocator<std::pair<System::UnicodeString, TSynchronizeChecklist::TItem *> >, 0> >::_Insert_nohint<...
(00184FE4) windows.storage.dll
(0002F12F) TCustomScpExplorerForm::SynchronizeApplyLocal
(0012964C) KERNELBASE.dll
(0002F753) TCustomScpExplorerForm::FullSynchronize
(00232FE2) System::Classes::TComponent::RemoveNotification
(0055B073) Dragdrop::TDragDrop::Notification
(001B3D56) System::Generics::Collections::TListHelper::DoRemoveFwd4
(00232FE2) System::Classes::TComponent::RemoveNotification
(001B3D56) System::Generics::Collections::TListHelper::DoRemoveFwd4
(00233027) System::Classes::TComponent::RemoveFreeNotification
(001B4CA0) System::Generics::Collections::TListHelper::InternalDoDelete4
(001B3D67) System::Generics::Collections::TListHelper::DoRemoveFwd4
(00232D46) System::Classes::TComponent::Remove
(0016AA7E) System::UTF8IdentToString
(0016B768) System::TMonitor::Enter
(00226CBE) System::Classes::RemoveFixups
(0005C3A1) ntdll.dll
(0012971D) KERNELBASE.dll
(0012976C) KERNELBASE.dll
(0012964C) KERNELBASE.dll
(0018D3DB) System::Sysutils::TryEncodeTime
(00033356) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(00045C55) USER32.dll
(00235394) System::Classes::_18364
(00045C55) USER32.dll
(00045E99) USER32.dll
(00045C97) USER32.dll
(0007477B) ntdll.dll
(00072424) ntdll.dll
(00135C5D) KERNELBASE.dll
(00135E93) KERNELBASE.dll
(0011E47D) nViewH.dll
(0002E039) UXTHEME.DLL
(00049CA4) USER32.dll
(0009F6CF) USER32.dll
(0009F6D8) USER32.dll
(00049D3D) USER32.dll
(000722CA) ntdll.dll
(0016CCFD) System::UStrFromPWCharLen
(0016DE4C) System::UStrCopy
(0053D326) Dirviewint::TDirViewInt::GetPath
(00069C5D) TScpCommanderForm::FullSynchronizeDirectories
(00446F3E) Vcl::Comctrls::TCustomListView::IsEditing
(00062E4E) TNonVisualDataModule::GetBusy
(0005BF16) TNonVisualDataModule::ExplorerActionsExecute
(003CA36A) Vcl::Controls::TControl::WndProc
(00049CA4) USER32.dll
(005702F9) Tb2hook::_16397
(000528DC) TNonVisualDataModule::ExplorerActionsUpdate
(00049CA4) USER32.dll
(00049AF7) USER32.dll
(00251F6C) System::Actions::TContainedActionList::ExecuteAction
(0016B13A) System::CallDynaInst
(003B6A79) Vcl::Actnlist::TCustomAction::Execute
(002343AF) System::Classes::TBasicActionLink::Execute
(00576A48) Tb2item::TTBCustomItem::Click
(0057693B) Tb2item::TTBCustomItem::ClickWndProc
(00235394) System::Classes::_18364
(0004F589) USER32.dll
(00045C55) USER32.dll
(000722CA) ntdll.dll
(00049A70) USER32.dll
(00045A68) USER32.dll
(000444FB) USER32.dll
(0004402B) USER32.dll
(004DDA87)

I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.