Hello Dany, I have the same problem too.
WP : v.3.7.1
MC4WP : v.1.4.4
I tested this with Chrome and Firefox.
For more information, when I check my API calls in the Mailchimp Api account page, I have two errors in the process (the same twice):
2013-11-27 08:45:27 GMT | X | nope | 93.x.x.x | lists/interest-groupings | json | 0.049s | WordPress/3.7.1; https://u… | 2.0 | (211)List_InvalidOption
Thanks for your help
