php iconv() : Detected an illegal character in input string

$str = mb_convert_encoding($str, "UCS-2LE", "JIS, eucjp-win, sjis-win");
$str = mb_convert_encoding($str, "EUC-JP', "auto");

例子：
$content = iconv("GBK", "UTF-8", $content);
$content = mb_convert_encoding($content, "UTF-8", "GBK");