Ram and Rom

I have this Wrong Messages.:confused:

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all; entity BUS_VHDL is

port

(

CS_ROM_n : out std_logic;

CS_OUT_LED_n : out std_logic;

bus_en_n : in std_logic; <<wrong---- Error (12014): Net "gdfx_temp0", which fans out to "BUS_VHDL:inst4|bus_en_n", cannot be assigned more than one value ----

Addr_bus : in std_logic_vector(7 downto 0)

);

End entity;

architecture rtl of BUS_VHDL is

Begin

process(Addr_bus, bus_en_n)

begin

if bus_en_n = '0' then

if unsigned(addr_bus) > 0 AND unsigned(addr_bus) < 16 then -- ROM adress

CS_ROM_n <= '0';

else

CS_ROM_n <= '1';

end if;

if addr_bus = "00010000" then -- OUT_LED adress

CS_OUT_LED_n <= '0';

else

CS_OUT_LED_n <= '1';

end if;

else

CS_ROM_n <= '1';

CS_OUT_LED_n <= '1';

end if;

end process;

end rtl;