got me on that one....
I have had no problem with those voices, and I have almost all of them.
I'm not understanding exactly what is happening. Is Hal using the Cepstral voice on startup then going silent? Or were you using a different voice at startup, then changed it to a cepstral voice and it didn't work?
If you have never heard the cepstral voice, then you might try using this:
http://cid-7d1b0521931256f1.office.live.com/self.aspx/.Public/Other/FixRegistry.zipIt fixes errors with sapi voices in the windows registry. I have used it personally. It is very safe, and only messes with sapi components....nothing else.
If you have heard the cepstral voice, but it doesn't work within Hal, then go to the windows "speech" config tool and select it as the windows default voice and see if you can hear it there. If you can then the voice is good and the problem is within Hal.
-hope that helps