I've installed mailchimp on a site (drupal 7.59, civi 4.6.33)
I have Created an API key in Mailchimp Copy/pasted API key to mailchimp settings in CiviCRM
And on clicking save/test get the following message
Could not use the Mailchimp API - API Key required. You will see this message If you have not yet configured your Mailchimp acccount.
Anyone else had this issue? Which blindingly obvious step have I missed out?