The Audition forum is your friend....
Moving this discussion to the Audition CS5.5 & CS6 forum.
Installation of Audition seemed to go ok. However, when it boots it reports that: "Loading the default input and output devices failed: MME internal device error..." I also get the error after I set the audio devices to either "ASIO" or "MME". Likewise, Audition will not output to the audio device (MOTU HD192 ASIO).
Need a little more information here to be sure, I think - the major bit being which OS this is, but I'm guessing W7. With W7 I had a dose of this with an E-Mu device, and what seemed to help most was making sure that everything was locked to run at one sample rate, and then absolutely sticking to it, but even that wasn't good with MME. Trouble with W7 and audio is that if the OS doesn't think that your signal is what it wants to see (and there can be several reasons for this), it resamples it to whatever it thinks is correct. As far as I can make out, Audition doesn't seem to be aware of this, and therefore thinks that there's an error in the driver, even when there probably isn't. The worst problem is that once it gets stuck in the loop of trying to change to the ASIO driver, it gets its knickers in something of a twist, and the only thing you can do is to restart it, and try again. Chances are that when it restarts, even though it said it has screwed up the change, it might actually have done it. It's frustrating, though. And absolutely make sure that your system sounds are turned off - another source of trouble, but it's been like that forever with M$.
What you have to strive to achieve though is running using the ASIO driver - this gets rid of a lot of the OS interference as well as lowering latency. With the E-Mu, this is the only way I can run it at all - the MME reports errors all over the place in Audition, even though other software appears to be able to use it. I never had any problems with this at all using XP, which I regard, in direct comparison, as considerably superior to W7 from an audio POV.
I have the same problem.
Since this thread is two years old and Audition has moved on a bit since then it would help if you could tell what the same problem is. Which audio interface? PC or Mac? What version of the operating system? Which version of Audition?