Try replacing the following function with this.
I also changed the shortcodes.
function wpex_process($content) {
$offset = 0;
$stag = '[more ';
$etag = '[/more]';
while(stripos($content, $stag, $offset)) {
// string to replace
$s = stripos($content, $stag, $offset);
$e = stripos($content, $etag, $s) + strlen($etag);
// inside data
$ds = stripos($content, ']', $s) + 1;
$de = $e - strlen($etag);
// style tag
$ss = $s + strlen($stag);
$se = $ds - 1;
$sstring = substr($content, $s, $e - $s);
$sdesc = substr($content, $ss, $se - $ss);
$sdata = substr($content, $ds, $de - $ds);
mt_srand((double)microtime() * 1000000);
$rnum = mt_rand();
$new_string .= '<a class="plsreadmore" id="showmore' . $rnum . '" onclick="this.className=\'hide\'" href="javascript:expand(document.getElementById(\'wpex' . $rnum . '\'))"> ... ' . $sdesc . ' </a>';
$new_string .= '<span class="wpex_div" id="wpex' . $rnum . '">';
$new_string .= '<script>expand(document.getElementById(\'wpex' . $rnum . '\')); expand(document.getElementById(\'wpexlink' . $rnum . '\'))</script>';
$sdata = preg_replace('^</br>sim', '', $sdata);
$content = wpex_str_replace_once($sstring, $new_string . $sdata . '<a class="plsreadmore" onclick="document.getElementById(\'showmore' . $rnum . '\').className=\'plsreadmore\'" href="javascript:expand(document.getElementById(\'wpex' . $rnum . '\'))"> ... close </a></span>', $content);
$offset = $s + 1;
}
return $content;
}