Help with database error

[baby41]

I get this error few times a week and would like to know if it is from my server or a coding 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)
/home/xxxxxxx/public_html/board/includes/class_core.php on line 311

[Opserty]

<a href="http://www.vbulletin.com/docs/html/cantconnect" target="_blank">Can't connect to local MySQL server through socket</a>