Try using v1.2.14 of this plugin. They still used the API key system in that release.
https://downloads.wordpress.org/plugin/mailchimp.1.2.14.zip
The OAuth implementation in the current version of the plugin is real broken.
Hi there alefattorini and chaoix,
Thanks for your posts. Our plugin developers are currently looking into and working on the connect issues some users have been experiencing. As soon as they get everything resolved they’ll be pushing out a fix. Thanks for your understanding and patience!
Let us know if there’s anything else we can assist with, and have a great day.
-Kath
Kath,
Putting my 2 cents in on the problem, allow your users to bypass the OAuth login and use the API keys system as a fallback if they choose to do so. A proper OAuth implementation should be implemented on top of an already working authorization system as a easy way to bypass fields, liek the API Key, not as a full replacement for an authorization system.
I have verified v1.2.14 of this plugin works on WordPress 4.0 and I will continue using it until some type of API Key system is implemented back into the plugin.
Matthew
