You may be unable to playback recorded voice memos after navigating to Extras > Voice Memos on your iPod. After selecting the desired voice memo and choosing play, the menu will revert to the Voice Memos selection screen. This can happen with:
To address this, update to the latest version of the iPod software. Use iPod (Click Wheel) Software 3.1.1 or later or iPod (color display) Software 1.2.1 or later. The iPod Updater 2006-01-10 includes these versions and can be downloaded here.
If you're not sure what iPod model you have, click here.