Right, I am trying to do it now so the 'image_url' cell is within the forum_post table, rather than the gallery_images.
When I insert the image_url cell into the INSERT... info all I return from my post when all the fields are filled in is blank - I check the MySQL db table forum_posts and it says no data was submitted. As soon as I remove image_url from there, and post it works fine. It worked for gallery_images and not forum_posts which is strange. I have installed the cell for both tables exactly the same.
$db->query("INSERT INTO " . $config['db']['prefix'] . "forum_posts (topic_id, user_id, ad_type, pet_type, breed, gender, colours, dob, available, price, message, username, first_name, last_name, phone, email, image_url, date_created, is_first) VALUES ($topic_id, $user_data[user_id], '$ad_type', '$pet_type', '$breed', '$gender', '$colours', '$dob', '$available', '$price', '$message', '$username', '$first_name', '$last_name', '$phone', '$email', " . time() . ", 1)");
$post_id = $db->insert_id();