Database error in vBulletin
 

mysql_connect() [<a href='function.mysql-connect'>function.mysql-connect</a>]: User already has more than 'max_user_connections' active connections
/includes/class_core.php on line 314

MySQL Error :
Error Number :
Request Date :
Error Date :
Script :
Referrer :
IP Address :
Username :
Classname : vB_Database
MySQL Version :

I often get a lot of emails with this message.
I am using vbulletin v4.1.6
I am asking for help.

Only thing you can do to prevent this in vBulletin is to make sure that Persistent Connections in vBulletin's config.php are turned off. Other than that you'll need to purchase a plan with more connections from your host or move to another provider.

The section in the config.php file is:
// ****** MASTER DATABASE PERSISTENT CONNECTIONS ******
// This option allows you to turn persistent connections to MySQL on or off.
// The difference in performance is negligible for all but the largest boards.
// If you are unsure what this should be, leave it off. (0 = off; 1 = on)
$config['MasterServer']['usepconnect'] = 0;

This should be set to 0 in your file.

to stand at 0
How much should I set it to?
The host says that 30 max connections are allowed on the server

You are restricted to a certain number of connections.
Ask your host what to do.
They might change it for you but they might ask you to choose another plan with them.(More expensive)