I am running Piwigo 2.2.3 with a lot of plugins.

I got the following error message:

Piwigo encountered a non recoverable error

[mysql error 2013] Lost connection to MySQL server at 'reading initial communication packet', system error: 0
Can't connect to server

#1    my_error /customers/9/2/4/......./httpd.www/piwigo/include/common.inc.php(129)
#2    include_once /customers/9/2/4/......./httpd.www/piwigo/admin.php(31)

What does it mean and what can I do?
Does anybody here know an answer?