Fatal Error when accessing admin section of subsite

I have a client who is receiving a fatal error when logging into their site. I am also encountering the error when I try to access their admin section when already logged in as the super admin. Here's the error:

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 1048576 bytes) in /home/igitaoj9/public_html/wp-includes/functions.php on line 443

Also, here's the section of the functions.php file that surrounds line 443:

/**
 * Serialize data, if needed.
 *
 * @since 2.0.5
 *
 * param string|array|object $data Data that might be serialized.
 * @return mixed A scalar data
 */
function maybe_serialize( $data ) {
	if ( is_array( $data ) || is_object( $data ) )
		return serialize( $data );

	// Double serialization is required for backward compatibility.
	// See https://core.trac.wordpress.org/ticket/12930
	// Also the world will end. See WP 3.6.1.
	if ( is_serialized( $data, false ) )
		return serialize( $data );

	return $data;
}

Client site is at http://newarknaz.org

I'm going in now to open up support access to my network.