You are already checking that the put/get succeeds in the original call:

$ftp->put($sub_log)
        or ErrorOut("put failed ", $ftp->message);
[download]

That will call ErrorOut if the put fails.
You then $ftp->quit to close the connection, and call $ftp->put after that in the if statement, which will try uploading the file again (fails because the connection is closed).