UTF8 Coding error

I get this error when trying to change my file to utf8 coding(if I change it with notepad++ it will be more problem)
ERROR LOADING FILE (DESTINATION.../C...) USING UTF8 CODING
can anybody help me?

I'm not sure I understand your question.

Maybe it's misunderstanding. WinSCP cannot convert an encoding of the file. The menu is to select in which encoding the file is, in case WinSCP auto-detection fails.

Though if you want to convert the encoding, you can cut whole file contents to a clipboard, save an empty file, switch the encoding to UTF-8 and paste the contents back and finally save the file again.