The 0 return value indicates the error during FtpCommand execution. What is returned by GetLastError()? You can use Apierror() function from Re: CopyFile API Problems with HP LaserJet 4000 Message #883304 to get a message for GetLastError() code.

>Requested Values :
>
>lnergebnis = 0
>THIS.cExtended_Message = ""
>
>>DECLARE INTEGER FtpCommand IN wininet;
> INTEGER hConnect,;
> INTEGER fExpectResponse,;
> INTEGER dwFlags,;
> STRING lpszCommand,;
> STRING dwContext,;
> INTEGER @ phFtpCommand