successes message but nothing get transferred

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We have been struggling for a while now to get Courier to work for us. Installation and licensing-issues have been resolved but now were stuck with the following error message when trying to transfer content between servers (nothing actually get transferred). Any suggestions or ideas?

The document has been transfered to the 'testservern' environment. Remember to login to the staging environment and publish it if necessary

Details:

    * 1, System.MissingMethodException: Method not found: 'umbraco.BusinessLogic.User[] umbraco.BusinessLogic.User.getAllByLoginName(System.String)'. at Umbraco.Courier.BusinessLogic.Messengers.Helpers.CMSNodeHelper.GetUser(Int32 id, String loginName, Boolean revertToMasterUser) at Umbraco.Courier.BusinessLogic.Messengers.Content.ContentMessenger.Extract(List`1 packages, User u)