I've heard a few times since Listen Up! began about folks having trouble fitting a part on a cd, even though all the audiobook parts are supposed to be small enough to burn to a CD-R. Here's what OverDrive suggests:
Sometimes, Windows Media Player thinks it can fit multiple parts on one CD, causing this error. We have found that isolating one part in Windows Media Player using the following steps resolves this error. Please ask them to follow these steps to accomplish that:
1. Close OverDrive Media Console and Windows Media Player.
2. Open "My Documents / My Media / [Book Title] ".
3. Right click on only the one part that will not burn.
4. Select "Add to Burn list".
5. Burn just this one part as usual.