Adobe Audition Play back

Just to be sure... in Multitrack you have to select the actual input you're going to use on the track that you're going to use it on; you can't rely on any defaults, especially if it's an external source:

And then you have to enable Record, and finally hit the Record button on the transport.

On the face of it, the only obvious reason for this to happen is that you may unintentionally not be using the mic plugged into the Focusrite - that sounds like the symptoms of recording with a laptop built-in mic. But to be sure, we'd need more information about how you are recording. Is this in Multitrack, or Waveform view. And what device driver are you using? Chances are that if it's not the ASIO one, your computer settings for sound may be being used as the defaults - especially if you haven't changed them. The advantage of using the ASIO driver is that you wouldn't have to change anything about the OS setup, because it bypasses most of it, and lets Audition talk to your Focusrite directly.