Disallow access to WordPress admin area for specific users

index.php

//===================================================
// DISALLOW ACCESS TO WPADMIN AREA FOR SPECIFIC USERS
//===================================================
function wps6543_no_admin_access()
{
    if ( 
        ! is_admin()
        || (
            is_user_logged_in()
            && isset( $GLOBALS['pagenow'] ) AND 'wp-login.php' === $GLOBALS['pagenow']
        )
    ) {
        return;
    }

    $redirect = isset( $_SERVER['HTTP_REFERER'] ) ? $_SERVER['HTTP_REFERER'] : home_url( '/' );
    if ( 
        current_user_can( 'CAPABILITY_NAME_HERE' )
        OR current_user_can( 'CAPABILITY_NAME_HERE' )
    )
        exit( wp_redirect( $redirect ) );
}
add_action( 'admin_init', 'wps6543_no_admin_access', 100 );