Sythesible code_Fatal error in a 2d array.

storing: for k in 0 to 10 loop
          inside: for l in 0 to 10 loop
           sum_of_square_all(k)(l)<=signed(ext(sum_of_square(inp1(k),inp2(l),"000000000000000000000000"),3*N));
          wait for 15 ns;
        end loop inside;
        match(k)<=find_min(sum_of_square_all(k));
     end loop storing;

library IEEE;
use IEEE.std_logic_1164.all;
use STD.TEXTIO.all;
use IEEE.std_logic_unsigned.all;
use IEEE.std_logic_arith.all;

entity tb_file_landmark is
  generic
		(N :integer := 8);
		port ( clk:in std_logic
		);
end tb_file_landmark;


architecture TB_ARCHITECTURE of tb_file_landmark is
file IN_1_VECTORS: TEXT open READ_MODE is "input_1.txt";
file IN_2_VECTORS: TEXT open READ_MODE is "input_2.txt";
file OUT_VECTORS: TEXT open WRITE_MODE is "output.txt";
--here
type matrix1_t is array(natural range<>) of signed(N-1 downto 0);
type big_matrix is array(natural range<>) of signed(3*N-1 downto 0);
type matrix2d is array (natural range<>) of matrix1_t(0 to 3);
signal sum_of_square_all: matrix2d(0 to 3);
signal inp1,inp2: matrix1_t(0 to 3);
signal a,b: signed(N-1 downto 0):= (others=>'0');
signal match:big_matrix(0 to 3);
signal flag:std_logic:='0';
signal k:integer range 0 to 100:= 0;
signal l:integer range 0 to 100:= 0;



--procedure sum_of_square( signal a,b: in signed(N-1 downto 0);signal  previous_sum:in std_logic_vector(3*N-1 downto 0); signal sum:out std_logic_vector(3*N-1 downto 0)) is
function sum_of_square( a1,b1: in signed(N-1 downto 0); previous_sum:in std_logic_vector(3*N-1 downto 0))return std_logic_vector is     
     variable temp_sum:std_logic_vector(3*N-1 downto 0):=(others=>'0');
     variable diff: signed(N-1 downto 0):=(others=>'0');
	   variable square_diff: std_logic_vector(2*N-1 downto 0):=(others=>'0');
begin
  temp_sum:=previous_sum;
  diff:=a1-b1;
	square_diff:=ext(diff*diff,2*N);
	temp_sum:=ext(temp_sum+square_diff,3*N);
  return temp_sum;
end sum_of_square;

function find_min(row: in matrix1_t(0 to 3)) return signed is
variable temp_min:signed(3*N-1 downto 0);
begin
  temp_min:=row(0);
  checking: for t in 1 to 3 loop
      if  (row(t)<temp_min) then
        temp_min:=row(t);
    end if;
  end loop checking;
  return temp_min;
end find_min;

begin
             
    process
        variable IN_BUF: LINE;
        variable OUT_BUF: LINE;
        variable a_var,b_var : bit_vector(N-1 downto 0):= (others=>'0');
        variable i,j: integer;
        
	--	variable c_var,d_var : bit_vector(N-1 downto 0):= (others=>'0');
  --variable sum_var:std_logic_vector(3*N-1 downto 0):= (others=>'0');
		
    begin
        i:=0;
        j:=0;
        while not ENDFILE(IN_1_VECTORS) loop
            READLINE(IN_1_VECTORS,IN_BUF);
            READ(IN_BUF,a_var);
            a<=signed(to_stdlogicvector(a_var));
            wait for 50 ns;
            inp1(i)<=a;
            i:=i+1;
        end loop;
        while not ENDFILE(IN_2_VECTORS) loop
            READLINE(IN_2_VECTORS,IN_BUF);
            READ(IN_BUF,b_var);
            b<=signed(to_stdlogicvector(b_var));
            wait for 50 ns;
            inp2(j)<=b;
            j:=j+1;
        end loop;
        flag<='1';
        wait;
    end process;
    
    process(clk)
       variable row:integer;
       variable column: integer;
    begin
      if (flag='1') then
        if (clk'event) then
          if ((k<=10) and (l<=10)) then
--############GETTING FATAL ERROR IN HERE##########
            sum_of_square_all(k)(l)<=signed(ext(sum_of_square(inp1(k),inp2(l),"000000000000000000000000"),3*N));
--############GETTING FATAL ERROR IN HERE##########
            k<=k+1;
            l<=l+1;
        end if;
      end if ;
  end if ;
end process;
    
end TB_ARCHITECTURE;