Mailchimp auto optin not working

i,ve Wpmudev mailchimp plugin network activated, integrated with Mailchimp with the API...i set auto optin to yes but no users are subscribed when they register...always i have to do import to import user to the mailchimp List. @Jack Kitterhing recommended me i checkout similar problem http://wordpress.org/support/topic/200invalid-mailchimp-list-id-b19ba5b197 i followed the steps but their solution didn't worked for me