From the DOS prompt run chkdsk and see if there's any file fragments. If so run chkdsk /f to correct.

At this point I would upgrade the voicemail to the latest version. If it's already there than just overlay it again.

If the voicemail is still erratic with saving messages and there were a lot of file fragments then there's a good chance the file structure may have some issues or the drive is failing. Reimage a new drive and replace. The Talkpath isn't really known for this unless there is a HDD problem. Even systems heavily fragmented usually run without issues.