The issue is that you are using
Col List Box()
and attempting to place non column names into the list.(i.e. Katie, Louise, etc. are not column names)
To do what you want, you need to use
List Box()
Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
col = {};
col[1] = column(dt, "name");
New Window( "List Box Example",
LstBox = List Box(, width( 250 )),
for(i=1, i<= N Rows(dt), i++,
LstBox << append(Eval(col[1][i]));
),
);
Jim