If you're using Skype for Windows with an Apogee USB interface and see the message "Your mic isn't working. Try another one", this most likely indicates a sample rate mismatch in the Windows Sound Control Panel. Ensure the selected sample rate is the same in these two locations.
- Control Panel Sound Playback (Select Apogee Interface) Properties Advanced
- Control Panel Sound Recording (Select Apogee Interface) Properties Advanced
See this Knowledgebase post for more details: