Mysql – get php_thesql.dll for Windows

How are you calling mysql_query()? I notice that you don't save the connection handle from the mysql_connect() call. It looks to me like the failing mysql_query() call is not using the connection you're making.

I recommend that you revise your code to do something like this:

function connect_db() {
    // Reads the config file
    include('system_config.php');

    if ($SYSTEM_DB_HOST == "") {
        return false;
    }

    $dbhandle = mysql_connect($SYSTEM_DB_HOST, $SYSTEM_DB_USER, $SYSTEM_DB_PASS);
    if ($dbhandle) {
        @mysql_select_db($SYSTEM_DB, $dbhandle);

        return $dbhandle;
    } else {
        return false;
    }
}

// ... invoke like this:
$dbhanle = connect_db();
if (!$dbhandle) {
    // handle failed DB connection
}

// later, whenever you need to run queries:
$result = mysql_query($querysql, $dbhandle);

This will ensure that the connection you make with mysql_connect is in fact the one that is used for the query. See if that changes anything; even if it doesn't, personally I think it's good practice to explicitly tell MySQL which DB connection you want to use.

I have this on my machine since upgrading. In my case, specifying 127.0.0.1 as the host instead of localhost does the trick.

One day it will bother me enough to really fix it :)

Edit regarding phpMyAdmin
Ah, phpMyAdmin... yes! I feel your pain. I HATE with a passion every time I am forced to re-install this app. It's a brilliant app when it works, but getting it into a working state has caused me a lot of grief over time.

In my personal experience, make sure all the required PHP modules are loaded and make sure your PHP sessions directory (as specified in php.ini) actually exists on the filesystem. If you change any of those, restart Apache.

Also in my experience, restarting Apache alone is not good enough - a browser restart is needed to properly clear the session.