Error (10028): Can't resolve multiple constant drivers for net "P[6]"

[Altera_Forum]

below are my code. 

when I compile, Error (10028): Can't resolve multiple constant drivers... is coming out, anyone knows what's the problem?   entity DU is  port ( clk, reset, ctrlA, ldA : in std_logic;  ctrlB, ldB, Psel, ldP : in std_logic;  dataA, dataB: in std_logic_vector (3 downto 0);  z, b0 : out std_logic;  P : buffer std_logic_vector (7 downto 0)); end DU; architecture Structural of DU is  signal Ain, Sum, dataP :std_logic_vector(7 downto 0);  signal A :std_logic_vector(7 downto 0);  signal B :std_logic_vector(3 downto 0);    component reg8 port  (ldP, clk, reset: in std_logic;  data: in std_logic_vector(7 downto 0);  Q : buffer std_logic_vector(7 downto 0));  end component;    component shiftLreg8 port  (d : in std_logic_vector (7 downto 0);  w,clk,reset,ctrlA,ldA: in std_logic;  Q : buffer std_logic_vector (7 downto 0));  end component;    component shiftRreg4 port  (d : in std_logic_vector (3 downto 0);  w, clk, reset, ctrlB, ldB: in std_logic;  Q : buffer std_logic_vector (3 downto 0);  b0 : out std_logic);  end component;   begin  c1: reg8 port map (ldP, clk, reset, dataP, P);  c2: shiftLreg8 port map (Ain,'0',clk,reset,ctrlA,ldA,A);  c3: shiftRreg4 port map (dataB,'0',clk,reset,ctrlB,ldB,B,b0);    Ain <="0000"&dataA;    process (clk,reset)begin  if reset='1' then   A <=(others=>'0');   B <=(others=>'0');  P <=(others=>'0');  elsif (clk'event and clk ='1') then   A <= Ain;  B <= dataB;  P <= dataP;  end if;  end process;    process (Psel) begin  if Psel='1' then dataP <= A+P;  else dataP <= (others=>'0');  end if;  end process;    process (B) begin  if B = "0000" then z <= '1';  else z <= '0';  end if;  end process;   end Structural;

[Altera_Forum]

Besides P also A and B multiple drivers. They are driven in two places, in the first process and in one of the component instances c1-c3. This is like shorting to logic outputs, it's not allowed by VHDL syntax rules. You have to decide, which side is intended to drive the respective nets.

[Altera_Forum]

thanks for info. the code can work now. 

 thanks a lot. :)