Apparently there is a problem synchronizing media files to the device. This type of error is usually seen in jailbrekeados devices (with cydia installed). To solve this create a new user, try to sync with this new user library. If not, reset the device. If still does not work then it must be some damage in your iTunes library that is causing the error file.
The firmware 3.0 ~ 3.1.0 is a known bug related to the synchronization and voice notes.