See if the following can help. (Note: I'm assuming that you are attempting to stream to an AirPort Express base station or Apple TV.)
Verify that your Mac is properly configured properly for streaming.
Verify that your AirPlay "speaker" is properly configured for steaming.
Check the following for the AirPort Express base station:
- Use the AirPort Utility to verify that the base station's name does not exceed 16 characters and does not include any spaces or special characters.
Verify that the Enable AirPlay option is checked (enabled) on the AirPlay tab.
While on this tab, verify that the AirPlay Speaker Name, like the base station name, does not exceed 16 characters and does not include any spaces or special characters.
Finally, you may want to consider downgrading the firmware on the base station. Try either of the following, as appropriate:
- Starting at 7.8, first downgrade to 7.6.9. Then down to 7.6.8
- Starting at 7.6.9, downgrade to 7.6.8
- Check the following for the AppleTV:
Settings > AirPlay > AirPlay: On
Settings > AirPlay > Allow Access: Same Network > Everyone OR Anyone on the Same Network
- For any third-party AirPlay "speaker," follow the manufacturers' recommendations for configuring the device for AirPlay.