WordPress: Notice:Object of class WP_Query could not be converted to int in on line

Your problem is here:

$featuredPosts = new WP_Query();
$featuredPosts->query('showposts=".get_option("mp_slides_no').'&category_name=".get_option("mp_featured_cat').'');

for($i=1; $i<=$featuredPosts; $i++) {

You’re creating a new instance of WP_Query to run a custom query and storing it in the $featuredPosts variable. But then you’re trying to use $featuredPosts as the upper limit of a for loop. This is what PHP is complaining about. Your $i<=$featuredPosts should be something more like $i<=count($featuredPosts->posts).

That said, you’re using actual Loop functions below that … which belong in a while($featuredPosts->have_posts()) loop instead of a regular for loop …