you could do
either first filter on {Cust.Active}=(Y)
then create dynamic parameter for {Cust.Name}
or
create dynamic parameter for
{Cust.Active} >>{Cust.Name}
to create a dynamic parameter
right click parameter fields >>new parameter>>
under list of values select dynamic >>
under value select {Cust.Name} or
select {Cust.Active} first line {Cust.Name} second line