Have struggled with this problem almost all day. I couldn't connect to another domain server using SQL Management Studio 2008 R2. Precisely, my other domain server is using Hyper-V and i called the server name as DOMAIN1. In this case i couldn't get access easily by using the server name but what i need is connect using the IP Address of DOMAIN1. In this case i defined the IP address of DOMAIN1 as 192.168.0.11
Make sure you can connect to DOMAIN1, add another IP Address. In this case, i am using IP 192.168.0.* so i can connect. For example i defined the IP address of my SQL Server computer as 192.168.0.9
Check the DOMAIN1 firewall, make sure it doesn't block connection from your computer. To set up Firewall, go to Windows Firewall with Advance Security.
Right Click on Windows Firewall with Advance Security and point to Properties > Domain Tab > and Allow inBound connection.
Run Command Prompt:
wait until SQL Management Studio 2008 R2 open by itself.
Once you get the Connect to Server Window. Fill in the Server Name as shown below:
Server type: Database Engine
Server name: 192.168.0.11\InstanceName
Authentication: Windows Authentication
Then click connect button.
Hope it works. Mine is working very well, now i can connect to my Hyper-V SQL Server. :) Good luck!