please be more specific about the SQL server you are using (Version, access mode, authentication, configuration).

 Hi Maximus,

Apart from your SQL Server being down (which it isn't according to your post) the hands-down most common reason that you will see that error is because there are too many connections to your SQL Server database.  Often this happens because either a rogue module is opening up too many connections to your SQL Server and not releasing the connections or someone is trying to brute force their way into a publiclly accessible SQL Server and they've opened up all the connections.

If you need help tracking down either what IP address is attacking you or what module is eating up your connections, please contact me directly and I will be glad to help.