500 Error on Twitter Authorization

Hi,

When signing in through Twitter, I get a 500 error once the oauth_token is returned. The URL when this occurs is (with unhelpful numbers omitted): https://sopresto.mailchimp.com/twitter/confirm?oauth_token=token&oauth_verifier=verifier

The message is:

error!

POST to https://example.com/index.php?social_controller=auth&social_action=authorized&salt=salt&p=postID failed with 500:

If I just fire off the sopresto.mailchimp.com URL in the browser, I get:

{"result":"error","response":"an error occurred"}

If I do the same to the second one, I get:

{"result":"error","message":"Invalid nonce"}

If I turn on WP_DEBUG and load up the URL that’s on my servers, I also see:

Notice: Uninitialized string offset: 0 in /myserverpath/wp-content/plugins/social/lib/social/controller/auth.php on line 95

Notice: Uninitialized string offset: 0 in /myserverpath/wp-content/plugins/social/lib/social/controller/auth.php on line 96

Notice: Uninitialized string offset: 0 in /myserverpath/wp-content/plugins/social/lib/social/controller/auth.php on line 100

Fatal error: Class 'Social_Service__Account' not found in /myserverpath/wp-content/plugins/social/lib/social/controller/auth.php on line 101

Any ideas? The debug log doesn’t really assist here.