Whenever you get this error, you need to check exactly what devices are connected to the computer. I had the problem that every time one of my colleagues came to the office, Flash Builder would all of a sudden not debug the AIR apps that I built using Flash Builder. The problem affects all ADT-based tools so this might be useful also if you're using Adobe Flash Professional or other tools (like xcode, java) or more to author your Android or iOS apps.
The fix is simple. Open a terminal window and type the following:
/Applications/YourApplicationName/eclipse/plugins/com.adobe.flash.compiler_220.127.116.119722/AIRSDK/bin/adt -devices -platform ios
The path to ADT will vary based on your machine, but if you're using some kind of Flash SDK, it'll be in a subfolder like the above. This command will show a list of the devices currently seen by the ADT and in my case, the phone belonging to my coworker showed up. His device wasn't physically connected to my machine, but since ADT supports debugging via wifi, it can still be used by the tool. For some reason, Adobe's tools will ignore the request to debug via cable and instead tries to connect to the Wifi device.