Blog runtime error for Cat

I'm using skip template to list other blog posts in that category

        <?php
        $categories = perch_blog_post_categories(perch_get('s'), array(
            'skip-template'=>true,


            ));

        if (count($categories)) {
        $cat_slugs = array();
        foreach($categories as $cat) {
        $cat_slugs[] = $cat['categorySlug'];
        }

        perch_blog_custom(array(
        'filter' => 'postSlug',
        'match' => 'neq',
        'value' => perch_get('s'),
        'category' => $cat_slugs,
        'sort-order'=>RAND,
        'count'=>3,
        'template'=>'blog/related.html',
        'section'=>'Recipes'

        ));


            }

    ?>

I'm now getting the error:

Array
(
    [type] => 2
    [message] => Invalid argument supplied for foreach()
    [file] => /var/sites/n/website.co.uk/public_html/perch/addons/apps/perch_blog/runtime.php
    [line] => 284
)

It's working fine on dev with the same files, so I don't know what's suddenly changed on the live site so it no longer works. The site is using Perch 2.4.9 and Blog 4.0.3 on both live and dev.

Many thanks