What are the steps:

1. Add New Host

2. Hos Type is Windows, Host Name - I use Pick option to get the servername (there is a DNS record), Host Group is WindowsGroup, Login Name is a local user with admin rights, Password is the pssword for that user

3. If I click on Verify Login it sees Successful so I can assume that the problem is not in credentials

4. Save - and the message Unable to add following hosts: Duplicate:[SERVERNAME] appears 

I have double checked my list of servers for both DNS name and IP and the server is not there. Can you please advise how to proceed with this server.

EventLog Analyzer's build number is 11003 and is running on Windows 2012 Standard.