WinSCP reports error when the custom command prints anything on the error output. You can possibly prevent that by output redirection:
call vboxmanage controlvm XXX savestate 2>&1
Though it is just suggestion, I haven't tried that.
Thanks for replying! :D The suggestion was very appreciated but your logs were so useful to the point that I just created a function to read the text in the logs and get the exact output made by the linux machine to provide an output if the command worked or not!:D
All I needed was to study your Guides!
Thank you so much for giving your Winscp the Absolute Return Statement that I need! :D
Also, thank you so much creating such a COOL(Astig) program! :D