getting user_id on register

I am trying to insert user_id to my accounts_table. But I am trying to get the user_ID from the user_table upon register.

I cant get the user_id (foreign key for my accounts_table) of the last registered user in the user_table which is what i need to be inserted on my accounts_table.

but when I var_dump($userData) i get value of null. and it says mysql_fetch_array() expects parameter 1 to be resource, boolean given why?

 $registerQuery = 'INSERT INTO   `user`(`firstname`,`lastname`,`email_address`,`password`,`mobile_number`,`address`,`birthdate`) VALUES (
    "'.ucfirst($firstname).'",
    "'.$lastname.'",
    "'.$emailaddress.'",
    "'.$password.'",
    "'.$mobile_number.'",
    "'.$address.'",
    "'.$birthdate.'"
    );';

    $qry = mysql_query($registerQuery); //INSERT TO DATABASE
    //echo $getuserIDQuery = 'SELECT `user_id` FROM `users` WHERE `email_address` LIKE \'%'.$emailaddress.'%\'';;
    echo $getuserIDQuery ="SELECT * FROM `users` WHERE `email_address` = '$emailaddress'";
    $getuserIDResult = mysql_query($getuserIDQuery);
    $userData = mysql_fetch_array($getuserIDResult) ;

    echo ' </br> ';
    var_dump($userData);
    echo ' </br> ';
    var_dump($emailaddress);
    echo '</br> ';
    echo $userData['user_id'];
    echo $emailaddress; //validation purpose only
    echo ' AND COUNT ='.count($getuserIDResult);     //check if found something 


    $accountQuery = 'INSERT INTO `accounts`(`user_id`,`balance`) VALUES (
    "'.$getuserIDResult.'",
    "'.$default_amount.'"
    );';

    $accountQry = mysql_query($getuserIDQuery);
}