If you try to create a new email campaign in Lime Go but get an "Unknow error" when you click the Save button, make sure that the MailChimp List is configured correctly.
For example, make sure that the list's setting Default 'from' email is set to an email address that has been verified by MailChimp. If not, you will get the "Unknown error".
Why doesn't Lime Go show a better error message then? It is because Lime Go get a generic error from MailChimp and don't know what is wrong.