Are you running iOS7? If so, you'll need to rebuild your app with the latest version of AIR (3.9). Apple made some changes in iOS7 that break the way the Scout companion app talks to your app, so you need to make sure you have both the latest version of the Scout companion app, and the latest AIR SDK, to fix the problem.
If not, check that the companion app can talk to Scout (i.e. it can connect to your machine, and reflects the settings you've checked in Scout). If it can't, then it's probably a network issue - make sure your firewall isn't blocking connections.
There are some more things you can try under the FAQ of the getting started guide (http://www.adobe.com/devnet/scout/articles/adobe-scout-getting-started.html), under "Why can't I get Flash Player to connect to Scout".
Thanks for that. I have updated to Air 3.9 and I am now getting output on Scout so that fixes the core issue. However I am not getting any trace output in the trace log. This is the same if I use the iOS simulator within Adobe professional or if I have published to a device. If I use the simulator I do see trace output in Adobe Flash professional itself but I am trying to track down a bug that only appears on the device so need output from there. I have checked that trace output is not being omitted. Any thoughts?
I just did a quick test to ensure trace output with iOS 7 is working. There is a compiler flag to enable/disable trace statements from release builds but I believe it is enabled by default so it should work unless you explicitly are disabling it for release builds (-omit-trace-statements).
Also, are you sure you are selecting the frame where you expect the trace output (or just select all)? Scout only shows the trace output from the currently selected frame(s), not all trace output.
hope that helps,
Thanks George - I simply was not selecting any frames! All sorted now, thanks.