This problem can occur if you've recently restored your device from a backup or switched to using another Palm device.

To fix this, you will need to do the following:

1. Clear your licenses. From within Pocket Tunes, tap the top of the screen to bring up the menu and select "Clear Licenses" from the 'Tools' menu.

2. Delete any protected audio files (tracks from libraries, on-line stores etc) from your device.

3. Transfer the protected audio files to your device again. This will refresh the licenses on your device.