[Plugin: WP Category Post List Widget] warning while display

Hmm for me it was fixing a typo for that error.
(v. 2.0.2 of the plugin at the time of writing)
Look in wp-content/plugins/wp-category-posts-list/includes/wp_cpl_output_gen.php at line 256 for:

$post_output .= ((true == $op['show_date'])? ' <span class="wp-cpl-date">' . _('Posted on: ', $wp_cat_list_itg_tans) . date('M jS, Y', strtotime($post->post_date)) . '</span>' : '');

and REPLACE it with this:

$post_output .= ((true == $op['show_date'])? ' <span class="wp-cpl-date">' . _('Posted on: ' . $wp_cat_list_itg_tans) . date('M jS, Y', strtotime($post->post_date)) . '</span>' : '');

The typo can be seen here _('Posted on: ',
that comma should be a dot (for those that aren’t coders the dot (period) here tell PHP to add things together)

Please update the plugin ASAP as I see a ton of these errors showing up in Google results.

Hello HallMarc, thanks for your reply. But the comma was intended to pass the translation domain string. The typo was _('Posted on:', $wp_cat_list_itg_trans) should’ve been __('Posted on:', $wp_cat_list_itg_trans).
Note the double underscore as the function name. This is a WP function which translates and returns string.

The typo has been fixed in V2.0.3

Wow, I completely missed that typo! Thank you for pointing it out. I kept thinking it was strange that it was complaining about receiving 2 params.