Hi,
I think that on your server is not installed PHP PDO libraries for mysql, you can contact your provider to install this libraries on server.

it was working befor

Try to delete this folder /plugins/jsn/socialnetwork/app/tmp/cache

if not work, please post me your site details, you can use the form below the reply in "Site Details" tab

Hi,
you not have installed PHP PDO drivers, if server is managed by you please install it, otherwise contact your provider to enable it.

PDO is a minimum requirement for this plugin (https://www.easy-profile.com/docs/91-system-requirements-socialnetwork.html).

If you are admin of server, please install PDO with this command with SSH:
Debian/Ubuntu Servers

sudo apt-get install pdo-mysql

Centos/RedHat Servers

yum install php-pdo php-mysqli

the error is:
Class 'PDO' not found in [/home/where/public_html/plugins/jsn/socialnetwork/lib/Cake/Model/Datasource/Database/Mysql.php, line 209]
2014-12-15 02:30:41 Error: [InternalErrorException] Internal Server Error

its already enabled

Hi,
this is only a panel to manage Apache web server options, but PDO is not installed.

if you go on Administration->System->System Information->PHP information you not see any reference of PDO Mysql Driver.

see screenshot from your PHP info.

You can contact your server administrator to install it.