Sometimes it could happen that WordPress convert the “&” symbol in the pagination into this: #038; Of course, then the pagination is not working anymore. To solve the problem you can add this function/code at the end of your functions.php file:
function sl_fix_pagination($link) {
return str_replace('#038;', '&', $link);
}
add_filter('paginate_links', 'sl_fix_pagination');

Posted in: Common errors