Did the music come from iTunes or another program that may have put DRM (Digital Rights Management) code on it? If so, you'd need to go through this process to use it in FCE, assuming it is only for home viewing:
http://fcpbook.com/Audio4.html
If it wasn't from iTunes, it may have been that the music you were using did not match the settings of your sequence. FCE only really likes audio files that are AIFFs at 32 or 48kHz. If this was the case, you could've gone through this process to convert the file to an AIFF that FCE likes:
http://fcpbook.com/Audio1.html -- In this case rendering should've worked as well.
Finally, it may have been that your preferences for real-time listening were set to the amount of tracks you were listening to!
As you can see, there are always multiple things that could go wrong, but it's great that it's working for you now. Good luck with your future projects!
Message was edited by: skalicki`