The merge process could not connect to the Publisher ' '. Check to ensure that the server is running. (
The error message is stated plainly:


  Login failed. The login is from an untrusted domain and cannot be used with Windows authentication


Try logging in to your Publisher as the replication agent account running on the subscriber (connecting from the subscriber through SSMS). There could have been changes to domain trusts, changes to domain membership, broken SPNs etc that could be causing this.

Validate your domains have a trust between them, your SPNs are configured correctly and that your replication accounts can actually log in to each instance. Also, double check that the accounts themselves are not disabled and\or have expired passwords.