8 Mb & 40000 lines of error log every day!!!

Hello,

I’ve noticed recently that the error_log exist in the root folder become so huge about 250mb and it’s almost containt of this two lines of errors :

— `WordPress database error Unknown character set: ‘utf-8’ for query SET NAMES ‘utf-8’ made by require, require_once, require_once, require_once, require_wp_db, require_once
— WordPress database error Unknown character set: ‘utf’ for query set names utf-8 made by require, require_once, include, include, dynamic_sidebar, call_user_func_array, WP_Widget->display_callback, YARPP_Widget->widget, yarpp_related, yarpp_cache_enforce,
yarpp_cache_keywords`

Please help me figue out what does that errors means, and how to stop it.

Thank You

My website