Как избавиться от такой ошибки?

procedure TForm1.BitBtn1Click(Sender: TObject);
const
press=20;
temperature=300;
temperature0=273;
press0=133;
sigma=1E-20;
k=1.38E-23;
gamma=0.1;
q=1.6E-19;
 
a=1;
b=1;
c=2;
e=1.6E-19;
ee0=8.85E-12;
var
i,N_max,PN,j:integer;
dx,V,dt,constanta,d,Ud,Ukatoda,n0,cs:real;
l,mu,Es,nn,mu0,N0e,N1:extended;
Ni:array [0..2000,0..1000] of real;
Ii: array [0..10000] of real;
F:TextFile;
 
//aa,bb:array [1..1999] of real;
//u,nevG,dz: array [0..2000] of real;
begin
mu0:=1*power(10,-2);
Es:=power(10,4);
d:=0.08;
N_max:=1000;
N0e:=1;
PN:=100;
dx:=d/PN;
mu:=mu0*(press0/press)*(sqrt(temperature/temperature0));
V:=mu*Es;
dt:=dx/V;
nn:=press/(k*temperature);
l:=1/(nn*sigma);
//Ud:=2800;
Series1.Clear;
AssignFile(F,'.\Ni.txt');
Rewrite(F);
for j:=0 to N_max do
  begin
    for i:=1 to PN do
      begin
        Ni[0,i]:=0;
        Ni[1,i]:=N0e*(exp((dx*i)/l))*(dx/l);
        N1:=gamma*Ni[j+1,1];
        Ni[j+2,i]:=Ni[j+1,i]+N1*(exp((dx*i)/l))*(dx/l);
        Write(F, Ni[j,i]);
      end;
    Ii[j]:=(Ni[j,1]*q)/dt;
    Series1.AddXY(j*dt*power(10,6), Ii[j],'', clRed);
    CloseFile(F);
  end;
 
end;

Ni:array [0..2000,0..1000] of real;

for j:=0 to N_max do
  begin
    for i:=1 to PN do
      begin
        Ni[0,i]:=0;
        Ni[1,i]:=N0e*(exp((dx*i)/l))*(dx/l);
        N1:=gamma*Ni[j+1,1];
        Ni[j+2,i]:=Ni[j+1,i]+N1*(exp((dx*i)/l))*(dx/l);
        Write(F, Ni[j,i]);
      end;
    Ii[j]:=(Ni[j,1]*q)/dt;
    Series1.AddXY(j*dt*power(10,6), Ii[j],'', clRed);
    CloseFile(F);
  end;