I understand you are unable to connect to your second Slingbox Pro-HD when you plug it in using the same configuration as the first Slingbox Pro-HD. Now the reason you are having this issue is because, in order to connect to a Slingbox, you have to run through setup for each specific Slingbox that you want to use. In order to configure that second Slingbox Pro-HD, you will want run through setup on Setup.Slingbox.com on a PC or Mac on the same network as the Slingbox. Once you have completed the setup process, you should be able to connect to your second Slingbox Pro-HD without an issue.
Hope this helps!
Sling Media Forum Moderation Team