Problems compiling with ISE Webpack 8.2.01i

[aijazbaig1]

Hello Freinds.
I am a newcomer to this forum and a newcomer to the field of programmable logic devices :itsme:. I am currently trying to teach myself VHDL. I hope to learn some VHDL before
the next semester starts.
My sole purpose as of now is not to actually synthesise stuff but just
to simulate the various designs that I may try to create. I am using
the xilinx ISE webpack 8.2 on a windows XP machine.
Below I am trying to implement a design called ones_cnt wherein the
counter just counts the number of ones in a 4 bit array and prints the
result in a binary format.To understand the concept of configuration
declarations I have declared multiple architectures and I am trying to
use the configuration declaration statement to select one the them.

Heres my code. Its a lil big may be but I hope you guys would have a
look.

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

---- Uncomment the following library declaration if instantiating
---- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity ones_cnt is
    Port ( A : in  STD_LOGIC_VECTOR (2 downto 0);
           C : out  STD_LOGIC_VECTOR (1 downto 0));
end ones_cnt;

architecture Algorithmic of ones_cnt is
begin
process(A)
    variable NUM: INTEGER range 0 to 3;
begin
    NUM := 0;
    for I in 0 to 2 loop
      if A(I) = '1'  then
        NUM := NUM + 1;
      end if;
    end loop;
    case NUM is
      when  0 => C <= "00";
      when  1 => C <= "01";
      when  2 => C <= "10";
      when  3 => C <= "11";
    end case;
end process;
end Algorithmic;

use work.all; ----- this is the line where the error is flaged!! see
below for details.
architecture STRUCTURAL of ones_cnt is
  component MAJ3C
    port (X: in BIT_VECTOR(2 downto 0); Z: out BIT);
  end component;
  component OPAR3C
    port (X: in BIT_VECTOR(2 downto 0); Z: out BIT);
  end component;
  for all: MAJ3C use entity MAJ3(AND_OR);
  for all: OPAR3C use entity OPAR3(AND_OR);
begin
  COMPONENT_1: MAJ3C
    port map (A,C(1));
  COMPONENT_2: OPAR3C
    port map (A,C(0));
end STRUCTURAL;

entity AND2 is
  port (I1,I2: in BIT; O: out BIT);
end AND2;
architecture BEHAVIORAL of AND2 is
begin
  O <= I1 and I2;
end BEHAVIORAL;

entity OR3 is
  port (I1,I2,I3: in BIT; O: out BIT);
end OR3;
architecture BEHAVIORAL of OR3 is
begin
  O <= I1 or I2 or I3;
end BEHAVIORAL;

use work.all;
entity MAJ3 is
  port (X: in BIT_VECTOR(2 downto 0); Z: out BIT);
end MAJ3;
architecture AND_OR of MAJ3 is
  component AND2C
    port (I1,I2: in BIT; O: out BIT);
  end component;
  component OR3C
    port (I1,I2,I3: in BIT; O: out BIT);
  end component;
  for all:AND2C use entity AND2(BEHAVIOR);
  for all:OR3C use entity OR3(BEHAVIOR);
  signal A1,A2,A3: BIT;
begin
  G1: AND2C
    port map (X(0),X(1),A1);
  G2: AND2C
    port map (X(0),X(2),A2);
  G3: AND2C
    port map (X(1),X(2),A3);
  G4: OR3C
    port map (A1,A2,A3,Z);
end AND_OR;

entity AND3 is
port(I1,I2,I3: in BIT;
		O: out BIT);
end AND3;
architecture BEHAVIORAL of AND3 is
begin
O <= I1 and I2 and I3;
end BEHAVIORAL;

entity OR4 is
port(I1,I2,I3,I4: in BIT;
		Z: out BIT);
end OR4;
architecture BEHAVIORAL of OR4 is
begin
Z <= X1 or X2 or X3 or X4;
end BEHAVIORAL;

use work.all
entity OPAR3 is
  port (X: in BIT_VECTOR(2 downto 0); Z: out BIT);
end OPAR3;
architecture AND_OR of OPAR3 is
  component AND3C
    port (I1,I2,I3: in BIT; O: out BIT);
  end component;
  component OR4C
    port (I1,I2,I3,I4: in BIT; O: out BIT);
  end component;
  for all:AND3C use entity AND3(BEHAVIORAL);
  for all:OR4C use entity OR4(BEHAVIORAL);
  signal A1,A2,A3,A4: BIT;
begin
  G1: AND3C
    port map (X(2),not X(1),not X(0),A1);
  G2: AND3C
    port map (not X(2),not X(1),X(0),A2);
  G3: AND3C
    port map (X(2),X(1),X(0),A3);
  G4: AND3C
    port map (not X(2),X(1),not X(0),A4);
  G5: OR4C
	 port map (A1,A2,A3,A4,Z);
end AND_OR;

architecture MACRO of ones_cnt is
begin
C(1) <= MAJ3(A);
C(2) <= OPAR(A);
end MACRO;

configuration Trial of ones_cnt is
for STRUCTURAL
end for;
end Trial;

Heres the log report generated by the compiler:
Started : "Check Syntax".
Running vhpcomp
Compiling vhdl file "E:/Xlinx_ISE/workbench/ones_cnt.vhd" in Library
isim_temp.
Entity <ones_cnt> compiled.
Entity <ones_cnt> (Architecture <algorithmic>) compiled.
ERROR:HDLParsers:3014 - "E:/Xlinx_ISE/workbench/ones_cnt.vhd" Line 55.
Library unit work is not available in library isim_temp.
Parsing "AND2_stx.prj": 0.38

Process "Check Syntax" failed


I do not know where am I going here as my VHDL code seems to be ok but
may be I am missing some tool-specific information here like having
certain libraries declared or something like that. I am completely new
to this field and I would sincerely appreciate if someone guides me
through the very difficult phase of getting started which I suppose you
guys might have gone through too in your yesteryears. :call2:

Looking forward to hearing from you,

Best Regards,
Aijaz.