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.
When WinSCP is left Idle with at least one active connection, it will eventually throw this error. The servers it is left connected to are usually shut off overnight. WinSCP is configured to try to automatically reconnect. The computer running WinSCP does not sleep or hibernate during this time.
WinSCP 5.9.6
Error message:
Invalid access to memory.
Stack trace:
(008689AA) System::AnsiStringBase::ThrowIfOutOfRange
(0086AA12) __roundToInt64
(008677CC) C5073_3
(00081CFF) ntdll.dll
(0006F87A) ntdll.dll.KiUserExceptionDispatcher
(004A5F97) Vcl::Imaging::Pngimage::TChunkIHDR::PrepareImageData
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.