Audio Import not importing

I've created 5 modules, all fine until I get to the last one. It has 26 slides, audio imported fine on the first 18. The 19th slide has no audio. Slides 20 - 26, no matter how many times I've tried it (many) and how many different formats of audio (2 - .wav and .mp3) and how many different names I've saved it under (3, in 3 different places, both locally and on a network drive) the same thing happens. No audio imported on Slides 20 - 26.

I created all the audio at the same time, and saved with the same criteria (.wav - PCM 8 bit mono). Articulate looks like it's going to do the import, but when I go to sync animations on Slides 20 - 26, there's no audio there. And I go back to the import screen, and the field where the path to the audio usually appears is blank for these slides. And when I listen to the presentation in preview mode, or in published mode, no audio.

I tried putting the sound files into the ppt, but they don't play when published.

Using PowerPoint 2007 and Articulate Presenter 09