i made this modification into the wppp.php to be like this
if ( has_post_thumbnail( $post['post_id'] ) ) {
$replace['%post_thumbnail%'] = get_the_post_thumbnail(
$post['post_id'], $instance['thumbnail_size']
);
that make the plugin able to crawl ANY post_thumbnail sizes that you have.
call it like this
<?php if (function_exists('WPPP_show_popular_posts')) WPPP_show_popular_posts("number=4&days=1&exclude=26101,26869&format=<a href='%post_permalink%' title='%post_title_attribute%'>%post_thumbnail%%post_title%</a>&thumbnail_size=new-depan-thumb"); ?>
so the “thumbail_size” is not accepting width/heigh in pixel but accepting post_thumbnail name that supported by your theme.
in my case, its called new-depan-thumb