Thanks for your report.
I have sent you an email with a debug version of WinSCP.
WINSCP VERSION: 5.7.1 (5235) Slovak lang
EARLIER VERSION: 5.7.0 working without errors.
OS: WinXP SP3 Englis Home
STEPS: I always edit my webpages online. I clicked on SAVE button and then message occured. I am running WinSCP and other two software which use network (oline cardgame: P****Stars and 888**** I need a bit adrenaline and lot of pauses for coding.)