As I don't have access to JMP14 I have to just guess what could be different.
Maybe loop isn't run at all -> add debug print for max
Names Default To Here(1);
dt = New Table("",
Add Rows(100),
New Column("ColumnA", Numeric, Continuous, Formula(Random Integer(50, 1000)))
);
max = Col Max(Column(dt, "ColumnA"));
Show(max);
For(i = 1, i <= max, i++,
Show(i);
);
other debug case, try loop without the table
Names Default To Here(1);
max = 10;
For(i = 1, i <= max, i++,
Show(i);
);
If JMP14 did have Debugger (and you can get that working as that might not be that easy) you could also try that
-Jarmo