why is this code wrong? generic or others?

[Zheyu.Gao]

library IEEE;
use IEEE.STD_Logic_1164.all, IEEE.Numeric_STD.all;
entity GCD is
generic (Width: natural:=8);
port (Clock,Reset,Load: in std_logic;
A,B: in unsigned(Width-1 downto 0);
Done: out std_logic;
Y: out unsigned(Width-1 downto 0));
end entity GCD;
architecture RTL of GCD is
signal A_New,A_Hold,B_Hold: unsigned(Width-1 downto 0);
signal A_lessthan_B: std_logic;
begin
----------------------------------------------------
-- Load 2 input registers and ensure B_Hold < A_Hold
---------------------------------------------------
LOAD_SWAP: process (Clock)
begin
if rising_edge(Clock) then
if (Reset = '0') then
A_Hold <= (others => '0');
B_Hold <= (others => '0');
elsif (Load = '1') then
A_Hold <= A;
B_Hold <= B;
elsif (A_lessthan_B = '1') then
A_Hold <= B_Hold;
B_Hold <= A_New;
else A_Hold <= A_New;
end if;
end if;
end process LOAD_SWAP;
SUBTRACT_TEST: process (A_Hold, B_Hold)
begin
-------------------------------------------------------
-- Subtract B_Hold from A_Hold if A_Hold >= B_Hold
------------------------------------------------------
if (A_Hold >= B_Hold) then
A_lessthan_B <= '0';
A_New <= A_Hold - B_Hold;
else
A_lessthan_B <= '1';
A_New <= A_Hold;
end if;
-------------------------------------------------
-- Greatest common divisor found if B_Hold = 0
-------------------------------------------------
if (B_Hold = (others => '0')) then
Done <= '1';
Y <= A_Hold;
else
Done <= '0';
Y <= (others => '0');
end if;
end process SUBTRACT_TEST;
end architecture RTL;

 

[Aiken]

What's the error?