We've had the best success with embedded attendant audio files when we stick to this format for the attendant and audio file naming. If you don't follow these, the IP Office ends up changing file names for you, and we've noticed that it can cause playback issues.
Attendant Name = No more than 12 characters for the Name and 8 characters for the Recording Name. The shorter the better.
I'd say, try rebuilding the attendant per the above rules, and if it doesn't help, send me the audio file and I'll test on my end.