That's because you are likely running a version of WordPress before 3.0. Please upgrade to the latest version. 3.x is a big step up from 2.x!

You've likely typed the wrong information into the API Key box. Don't type in your username; you need to paste in your MailChimp API Key, which you can find by logging into your MailChimp account and clicking on "My Account" in the upper-left and choosing "API Key and Info".

Check to see if you are requiring any fields in MailChimp. If you do not send that data over from your WordPress site, then MailChimp will reject the update. For example, if you require first and last names, then you should use another plugin like Register Plus Redux to require users to enter first and last name. Otherwise, AutoChimp will fail to sync with your mailing list because there's simply no first and last name data for your required fields. Be sure to check the "Patch Register Plus Redux" checkbox in the AutoChimp settings after you activate Register Plus Redux.

AutoChimp is not a visual plugin. It does all it's work behind the scenes keeping your blog users in sync with your mailing list. If you are looking for a registration widget for MailChimp, search for "MailChimp List Subscribe Form" on the WordPress plugin site.

Just go to http://www.wandererllc.com/company/plugins/autochimp/ and follow the instructions.

MailChimp, like all other major email campaign managers, sends newly subscribed members a confirmation email. So, you must wait until the new subscriber receives, accepts, and confirms the new subscription before you see them appear in your mailing list. AutoChimp will trigger the confirmation email right away. However, you can opt to bypass this double opt-in by checking the “Bypass MailChimp double opt-in” check box.

Sometimes, plugin output may not render properly in your campaigns generated from posts. This is usually because the plugin doesn’t have access to information it needs until it is displaying its output on the screen for an end user. The best suggestion in this case is to learn which of your plugins are problematic (most are fine) and adapt accordingly. We’ll look for ways to improve this in the future too.

Your campaign formatting may appear differently than your post formatting. This is because your post uses formatting files that belong to your WordPress theme that your campaign doesn’t have access to. The best thing you can do is to use the HTML tab in the “Post Edit” page to add specific HTML instructions. MailChimp campaigns speak HTML very well.

Updating your mailing list when a user changes their profile has the potential to be problematic. If you have alternate UIs or non-standard ways of updating users, then the correct sequence of calls may not happen and, as a result, the subscribed user will not be found in your MailChimp mailing list. This is not the case for most WordPress users, but it’s good to be aware of. The reason? There is the notion of an “old email” and a “new email”. The old email must be fetched before the new email in order to find the equivalent MailChimp user and if the plugin doesn’t correctly pick up the old email, then it will be impossible to update a member. The old email is fetched when the user’s profile page is displayed. The new email is saved when the user commits the update.

Yes, you’re right! This has been fixed in version 1.01. This is more of a versioning problem with MailChimp’s API. Read more here: http://www.wandererllc.com/company/2010/12/autochimp-1-01/

Visit MailChimp's site which lists various error codes that can occur: http://apidocs.mailchimp.com/api/1.3/exceptions.field.php