The "mode" parameter of the PHP5 ftp_chmod function is an integer value that is supposed to be given as an octal number, like the argument for the "chmod" command line tool.
Thus the sprintf must use the %o formatting character, so that the passed integer value is really represented as an octal number to the CHMOD site command for the FTP server.
So, IMHO, rabin's version is correct (it definitely worked for me).