Проблемы при установке

function utf8_substr($str, $offset, $length = null)
{
    if (function_exists('mb_substr')) return mb_substr($str, $offset, $length, 'utf-8'); #(PHP 4 >= 4.0.6, PHP 5)
    if (function_exists('iconv_substr')) return iconv_substr($str, $offset, $length, 'utf-8'); #(PHP 5)
    preg_match_all('/(?>[\x09\x0A\x0D\x20-\x7E]           # ASCII
                      | [\xC2-\xDF][\x80-\xBF]            # non-overlong 2-byte
                      |  \xE0[\xA0-\xBF][\x80-\xBF]       # excluding overlongs
                      | [\xE1-\xEC\xEE\xEF][\x80-\xBF]{2} # straight 3-byte
                      |  \xED[\x80-\x9F][\x80-\xBF]       # excluding surrogates
                      |  \xF0[\x90-\xBF][\x80-\xBF]{2}    # planes 1-3
                      | [\xF1-\xF3][\x80-\xBF]{3}         # planes 4-15
                      |  \xF4[\x80-\x8F][\x80-\xBF]{2}    # plane 16
                     )
                    /xs', $str, $m);
    if ($length !== null) $a = array_slice($m[0], $offset, $length);
    else $a = array_slice($m[0], $offset);
    return implode('', $a);
}