When using the hotkey combinations command + backtab (increase impact level) or command + tab (decrease impact level) to change the dot impact, the speech "error" is heard.
The dot impact commands are only suypported on certain models of the Mountbatten. In general only the older blue Mountbattewn models suport the command. This does not apply to the newer Whisperer (grey case) models which do not support adjustment of dot impact level.