The issue you are having is that you are retrieving a character string variable from your Button Box, but your list of column names are expressions
para_num = "zippy";
colnameslist = {BP 8M, BP 12M, BP 6M, BP 8W, BP 12W, BP 6W, BP 8F, BP 12F, BP 6F};
If you just specify to have the colNamesList returned as strings, your code will work
colNamesList = dt << get column names( continuous, string );
Jim