I was sent this fix by Winhost support ticket staff: http://www.geeksvilla.com/download-f…oes-not-exist/
the specific code given :
define(‘WP_TEMP_DIR’, ABSPATH . ‘wp-content/’);

should be placed in wp-config down in the section commented as such:
/** define(‘WP_TEMP_DIR’,$path’); **/

upload it to your WP install root.
mine began allowing plugin updates from the Dashboard plugins page again. Whew!