PHP警告：preg_replace_callback（）：需要参数2 [重复]

I've been getting 503 errors on my Wordpress website. I turned on debug mode and this is what showed up:

PHP Warning: preg_replace_callback(): Requires argument 2, 'stripslashes(strstr("\2\5","rel=\class=") ? "\1" : "<a\2href=\"\3\4\"\5 rel=\"colorbox\" class=\"colorbox\"><img")', to be a valid callback

Here is the code it's referring to:

function ace_colorbox_replace($string) { 
$pattern = '/(<a(.*?)href="([^"]*.)'.IMAGE_FILETYPE.'"(.*?)><img)/i';
$replacement = 'stripslashes(strstr("\2\5","rel=\class=") ? "\1" : "
<a\2href=\"\3\4\"\5 rel=\"colorbox\" class=\"colorbox\"><img")';
return preg_replace_callback($pattern, $replacement, $string);
}

I know there's some outdated code that I did update a while back... But now it's having this error. I'm not too familiar with simple PHP, but I have some experience. This is out of my comfort zone... Any help is appreciated.

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