<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 6.5.5

Error message:
Failed to write ImageList data to stream

Stack trace:
(0048B1B1) Vcl::Imglist::TCustomImageList::WriteData
(0059A29A) Pngimagelist::TPngImageList::WriteData
(00598C73) Pngimagelist::TPngImageList::Assign
(00E102B9) TGlyphsModule::UpdatePixelsPerInch
(00E10032) TGlyphsModule::SetLargerToolbar
(0000A76F) TCustomScpExplorerForm::ConfigurationChanged
(0000AF06) TCustomScpExplorerForm::RestoreParams
(00059ECE) TScpCommanderForm::TScpCommanderForm
(004B1D16) Vcl::Forms::TApplication::CreateForm
(00E0B21B) _SafeFormCreate
(000033BB) wWinMain
(00EF5205) __wstartup
(0006C5D9) ntdll.dll
(0006C55C) ntdll.dll

The problem happens rarely. I cannot reproduce it.

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.

<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 5.13.5

Error message:
Failed to write ImageList data to stream

Stack trace:
(001A7C5E) Vcl::Imglist::TCustomImageList::WriteData
(004A8D82) Pngimagelist::TPngImageList::WriteData
(004A7861) Pngimagelist::TPngImageList::Assign
(008684DC) TGlyphsModule::SetPixelsPerInch
(00868233) TGlyphsModule::TGlyphsModule
(000E2C38) Execute
(000024B4) wWinMain
(008BCD75) C4973_0
(00062058) ntdll.dll.RtlValidSecurityDescriptor
(00062025) ntdll.dll.RtlValidSecurityDescriptor

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.