Premiere to Audition doesn't seem to work

The basic starting position with Audition and Premiere is that you should have the current version of each on your machine, and fully licenced. The 'current version' part is quite important, as the interchange between the two is still being worked on to an extent, and versions are 'matched' to each other. It's not the case that it definitely won't work otherwise, but your chances of getting a good result diminish somewhat. Also it's quite important to recognise what will and won't transfer, and what the limits to what you can realistically achieve are. For instance, if I wanted to extend an audio file like a background sound over an entire video, I wouldn't use the route you are trying at all - I'd just open the audio file in Audition, extend it to the length you want it first, save it, and then just import the resulting file into Premiere. Why? Because it's non-synchronous, and it's simply easier than transferring files back and forth. Where I find the 'open in Audition' route to be far more use is with synchronised clips that you need to manipulate.