A stacked bar chart has the same requirement that a line chart with several lines has: You need a separate data series of Y-axis values for each line or each component of your stacked bar.
One way to get that is with a series of calculation fields that only return a value for a specific response such as:
If ( Responses::Answer = "Always" ; 1 )
You can then set up summary fields that total each of these different calculation fields to return a count of the number of responses with that answer and each of these summary fields can be specied for a different y-axis data series in your stacked bar chart.
Thanks again, that has solved my problem although I did struggle to get the chart to display a percentage rather than the total number of responses.