I really need help !

[Milobil]

First, sorry for my english (i'm not).

Yesterday, i wanted to access to my forum, but i saw database error in the index page, so i I logged on my mailbox (gmail) and vbulletin (my forum) sent me some errors for database like this :

Database error in vBulletin :

mysql_connect() [<a href='function.mysql-connect'>function.mysql-connect</a>]: User xxx already has more than 'max_user_connections' active connections
/home/ah40607/web/www/forum/includes/class_core.php on line 317

MySQL Error   :
Error Number  :
Request Date  : Monday, July 23rd 2012 @ 02:19:38 AM
Error Date    : Monday, July 23rd 2012 @ 02:19:38 AM
Script        : http://www.myforum.com/forum/css.php?styleid=3&langid=1&d=1342049041&td=ltr&sheet=forumbits.css,forumhome.css,options.css
Referrer      : http://www.myforum.com/forum/forum.php
IP Address    : XXX.XX.XX.XXX
Username      :
Classname     : vB_Database
MySQL Version :

Or this :

Database error in vBulletin 4.2.0:

Invalid SQL:

                        SELECT IF(thread.visible = 2, 1, 0) AS isdeleted,


                        NOT ISNULL(subscribethread.subscribethreadid) AS issubscribed, emailupdate, folderid,
                        post.pagetext AS description,
                        thread.*


                        FROM thread AS thread

                        LEFT JOIN subscribethread AS subscribethread ON (subscribethread.threadid = thread.threadid AND subscribethread.userid = 0  AND subscribethread.canview = 1)


                        LEFT JOIN post AS post ON(post.postid = thread.firstpostid)


                        WHERE thread.threadid = 406;

MySQL Error   : MySQL server has gone away
Error Number  : 2006
Request Date  : Monday, July 23rd 2012 @ 01:59:27 AM
Error Date    : Monday, July 23rd 2012 @ 02:14:13 AM
Script        : http://www.myforum.com/forum/newreply.php?do=newreply&t=406
Referrer      :
IP Address    : XXX.XX.XX.XX
Username      : Unregistered
Classname     : vB_Database
MySQL Version :

So after i saw those errors, i went to my host and connect to mysql database using phpmyadmin and miraculously, my forum was now accessible and on...

I just wanted to know what are those errors and what i have to do to avoid this in the future.

Thank you for your help.