using subtype

good morning,

am obliged to define the type t_pnet_data before the architecture to be 
able to use it in ports types, this is a part of the code :



library ieee;
use ieee.std_logic_1164.all;


subtype t_pnet_data is std_logic_vector(7 downto 0);

type net_frame is record
   low : t_pnet_data;
   high : t_pnet_data;
end record net_frame;

entity pnet_write is
    port(
        p_net_data_in     : in std_logic_vector(7 downto 0);
        p_net_data_valid  : in std_logic;
        p_net_data_read   : out std_logic;
        p_cpu_data_out    : out std_logic_vector(7 downto 0);
        p_cpu_data_valid  : out std_logic;
        p_cpu_data_read   : in std_logic;
        p_cpu_parity      : out std_logic;
        p_retx_data_out   : out net_frame;
        p_retx_data_valid : out std_logic;
        p_retx_data_read  : in std_logic
        );
end pnet_write;

architecture write of pnet_write is
    begin
- - - - - -


and this the error :

** Error: C:/Modeltech_6.2d/examples/pnet_write.vhd(5): near "subtype": 
expecting: ARCHITECTURE CONFIGURATION ENTITY LIBRARY PACKAGE USE


what can i do ?!

best regards

Wafa