Frank Goossens on "[Plugin: Autoptimize] Changing the wp-content path to top level"

Ah, you'll also have to change autoptimize_cache_dir (which uses WP_CONTENT_DIR) to tell AO where to write the files (vs autoptimize_cache_url which is for AO to inject the correct URL's in the HTML). This is how it is set by default:

if (is_multisite()) {
	$blog_id = get_current_blog_id();
	define('AUTOPTIMIZE_CACHE_DIR' , WP_CONTENT_DIR.AUTOPTIMIZE_CACHE_CHILD_DIR.$blog_id.'/' );
} else {
	define('AUTOPTIMIZE_CACHE_DIR',WP_CONTENT_DIR.AUTOPTIMIZE_CACHE_CHILD_DIR);
}

frank