That is because you cannot install the Edge Server roles on ANY other host with OCS services installed. The Edge Server must be a separate physical host that is not a domain member and is located in a perimeter network of some sort. This is a VERY basic requirement and is covered many times in the product documentation.
I don't mean to be rude but I see you have a lot of posts recently and seem to be struggling with this deployment. I HIGHLY recommended you take a few hours and read through as much of the product documentation as possible. OCS is quite complicated and you can save yourself a ton of headaches by getting some of that stuff figured out beforehand. Trust me, I tried it the hard way the first time as well :)
Really read closely through the Planning and Architecture sections:
http://technet.microsoft.com/en-us/library/dd250572(office.13).aspx
Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS
