Constant MySQL Error

[Bradley_Wint]

So I keep getting this MySQL error.

Database error in vBulletin :

mysql_connect() [<a href='function.mysql-connect'>function.mysql-connect</a>]: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) /myserver/public_html/includes/class_core.php on line 311

MySQL Error   : 
Error Number  : 
Date          : Sunday, April 13th 2008 @ 02:10:57 PM
Script        : http://level2gaming.com/memberlist.php?ltr=P&order=ASC&sort=username&pp=50
Referrer      : 
IP Address    : 66.249.70.220
Username      : 
Classname     : vB_Database
MySQL Version :

I notice the only sites ips that encounter this are search engines MSN Live and Google. Any reason why this happens?