Error 10029: Constant Driver, Error 10028: Can't resolve multiple constant drivers

Hi, I am trying - processing/start/start analysis and elaboration - in Quartus 2 for the following VHDL code:

code:

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

entity ber_count is

generic ( size : integer := 128);

port ( clk : in std_logic;

--clkp : in std_logic;

enc_valid : in std_logic;

dec_valid : in std_logic;

enc_data : in std_logic_vector ((size-1) downto 0);

dec_data : in std_logic_vector ((size-1) downto 0);

error_count : out std_logic_vector (7 downto 0)

);

end ber_count;

architecture behavioral of ber_count is

signal enc_buf, dec_buf : std_logic_vector ((size-1) downto 0);

signal ecount : integer := 0;

signal new_dec_data, new_enc_data : std_logic;

signal global_frame_count : integer := 0;

signal err : std_logic;

begin

load_encoded_data: process(enc_valid)

begin

if rising_edge(enc_valid) then

enc_buf <= enc_data;

new_enc_data <= '1';

global_frame_count <= global_frame_count + 1 ; -- if needed, we can use this value to calculate BER

end if;

end process;

load_decoded_data : process(dec_valid)

begin

if rising_edge(dec_valid) then

dec_buf <= dec_data;

new_dec_data <= '1';

end if;

end process;

count_errors: process (clk)

begin

if rising_edge(clk) then

if (new_enc_data = '1'and new_dec_data = '1') then

new_enc_data <= '0';

new_dec_data <= '0';

for i in 0 to (size-1) loop

err <= (enc_buf(i) xor dec_buf(i)) ;

--if(enc_buf(i) = dec_buf(i)) then

if (err = '1') then

ecount <= ecount + 1 ;

end if;

end loop;

end if;

end if;

end process;

error_count <= std_logic_vector(to_unsigned(ecount, error_count'length)); -- typecast integer into std_logic_vector

end behavioral;

code description: As you might have guessed this is code for an error counter module which buffers output frame from encoder and decoder, and compares

the two frames to find number of errors.

I am relatively new at VHDL, so the code might be a bit dirty (actually very dirty -_-).

errors: These are the errors I am getting : Error (10028): Can't resolve multiple constant drivers for net "new_dec_data" at ber_count.vhd(50)

Error (10029): Constant driver at ber_count.vhd(41)

Error (10028): Can't resolve multiple constant drivers for net "new_enc_data" at ber_count.vhd(50)

Error (10029): Constant driver at ber_count.vhd(31)

The indicated lines in the error message are denoted in Arial Black font in the code.

How do I resolve this problem ?

Thanks

Leo