When trying to set up master to master replication from Server A to Server B, the replication user can login from A to B, but not the other way. The error thrown out by MySQL:
ERROR 1130 (HY000): Host '
Things to check:
1. Replication user password and host
2. Ability to ping the remote server
3. nslookup the remote server and then nslookup the ip for the reverse lookup
The last one solved the problem.