My experience thus far:
I have the Mackie control surface "connecting" issue between my desktop PC (Win7 64 bit) running Sonar X1 Producer (X1c) and AC-7 running on my iPad2. rtpMIDI works as advertised and absolutely is not the problem. AC-7 Core (running on iPad2) is also not the problem for sure. In troubleshooting this !@#$% problem, I decided to install SOnar X1 and rtpMIDI on my laptop (Win 7 64 bit) and see if that worked. It did without any issues. Start up rtpMIDI, start up AC-7 and rtpMIDI connects. Then start up X1, start a new project, and hit reset on the AC-7 and instant connection. This means AC-7's OK, my network is OK, and rtpMIDI is OK. It must be some obscure setting in Sonar. I believe that it cannot be any sort of network/security/firewall issue because rtpMIDI connects fine. I can't believe it's a Windows 7 issue because I have the same OS on both platforms. I'm gonna dig a little deeper here, but if any of you guys have found the silver bullet, please post up here so I can stop pulling what little hair I have left out!