How are you running your script? For me it will just print it to the log and not interrupt the script execution (using JMP18.0.1 on Windows 10 so might be different on OSX).
Names Default To Here(1);
dt = As Table(J(10000, 10000));
dt << new column("A", Character, Nominal, Set Each Value("A"));
dt << new column("B", Character, Nominal, Set Each Value("B"));
dt << new column("C", Character, Nominal, Set Each Value("C"));
dt << new column("D", Character, Nominal, Set Each Value("C"));
dt << new column("E", Character, Nominal, Set Each Value("C"));
dt << new column("F", Character, Nominal, Set Each Value("C"));
cols = dt << Get Column Names("Continuous", String);
dt_stacked = dt << Stack(columns(eval(cols)));
You could try Batch Interactive(1) and Batch Interactive(0) commands
Names Default To Here(1);
dt = As Table(J(10000, 10000));
dt << new column("A", Character, Nominal, Set Each Value("A"));
dt << new column("B", Character, Nominal, Set Each Value("B"));
dt << new column("C", Character, Nominal, Set Each Value("C"));
dt << new column("D", Character, Nominal, Set Each Value("C"));
dt << new column("E", Character, Nominal, Set Each Value("C"));
dt << new column("F", Character, Nominal, Set Each Value("C"));
cols = dt << Get Column Names("Continuous", String);
Batch interactive(1);
dt_stacked = dt << Stack(columns(eval(cols)));
Batch interactive(0);
-Jarmo