Hello,
I do not know the exact reason for that but you can find out by checking these points in your program.
First of all, are you setting the 'handle' import parameter with the same value that is exported from the FM 'FTP_CONNECT' ?
If so, is the folder (the path that you want to put that file in) really exist on the FTP server? Can you look it up on using FileZilla or any other FTP client program that you are using?
And also you should set character_mode parameter as 'X' in most cases. Have you done that?
I hope one of these questions will help you.
Regards,
Arman.