The server is reachable by my client since, with my application, i can get file, get directory listing, navigate (ChDir, ChUp) etc ...
I cannot only put file. More on the same PC as my application i can put file manually using FTP in Win XP command line.
Server is a VMS one. For the moment i didn't have any control on server, so I cannot get log files from it.
Finally, I tried to use both put methods, with append flag and without it. Using append method with true flag, the file is created on the server but contains nothing.