Well, I haven't worked with merge replication per se, but I've seen this type of error in other replication scenarios.
If I recall correctly, we need to make sure the account the SQL Agent service is running under on the publisher has proper (administrative) access on the target (subscriber) instance(s).
You may need to add that account manually to the "System Administrator" role on the subscriber instances. Think replication uses the credentials of the SQL Agent account to authenticate.
Buenos dias!
- john