If you are using a Mac and tracks in your library seems to be playing too fast in the Offline Player then this is to do with the playback sample rate of the default sound device (your computer's sound-card). To fix this set the internal sound-card playback sample rate to 44.1K.
To change it do the following:
1. Close all software
2. Go to your Finder -> Applications -> Utilities -> Audio/MIDI Setup
3. Set the internal sound-card to 44.1k (and not 48k).
Now your music should play back at the normal speed.