siteurl value getting populated with junk in wp_options table

My website http://www.blackpepperstudio.com was getting this error on every page :

Catchable fatal error: Object of class WP_Error could not be converted to string in /home/juhisheth/public_html/wp-includes/default-constants.php on line 102

After a lot of troubleshooting I realized that this is coz the siteurl value in wp_options table is getting populated with the following junk :

O:8:"WP_Error":2:{s:6:"errors";a:1:{s:30:"wpdb_get_table_charset_failure";a:1:{i:0;s:0:"";}}s:10:"error_data";a:0:{}}

I changed the value to : http://www.blackpepperstudio.com and everything started working again. The problem is, this issue is recurring and comes up even when I don’t do any changes to the website. How do I resolve it?