Those errors sound like the Speakup driver is sending unrecognized commands to your synthesizer. Further, it sounds like the error messages typical of a Dectalk Express. Did you specify that you are using a Dectalk Express? In other words, "speakup_synth=dtlk" as your boot parameters? I don't know of any other reason why you'd be getting errors from the Dectalk unless you've found a bug in the Dectalk Express driver.
