On the MailChimp settings panel, there is an error immediately after the
“Current MailChimp Status” field:
Catchable fatal error: Object of class stdClass could not be converted to string in ####/wp-content/plugins/mailchimp-framework/mailchimp-framework.php on line 473

The mailchimp userid and password are not correct for the site — but I’m unable to change them because there’s no “save” button. The fatal error stops the plugin before the “save” button is shown, it seems. Perhaps saving the correct values would remove the error?

After I navigate around the admin area a bit, I get an error about number of login attempts, and the mailchimp account gets locked for awhile.

Maybe uninstalling the plugin completely will remove the mailchimp settings, so the error won’t show up, and I’ll be able to input the correct settings.

I’ve installed this plugin on two instances of WordPress. Each time, the Settings page fatal errored and I wasn’t able to update the API key, password, etc.

The fix was to comment out Line 823:
return $this->callServer( $args );
and add
return "Everything's Chimpy!"

I was able to access the Settings page again. Once I updated my Mailchimp settings, I reverted the fix and I didn’t get the fatal error anymore.

If you do this, make sure to revert the fix too or you’ll lose ping() functionality.