Ошибка: Is not a valid floating point value

procedure TForm1.SpeedButton4Click(Sender: TObject);
var k,i,n: integer;
s,g1,g2,R1,R2,A1,A2:real;
begin
  n:=SG1.RowCount-1;
  k:=SG4.RowCount-1;
sx:=0;for i:=1 to n do sx:=sx+StrToFloat(sg1.Cells[1,i]);
sx:=sx/n;
s:=0;for i:=1 to n do s:=s+sqr(StrToFloat(sg1.CelLs[1,i])-sx);
s:=s/n;
g1:=0;for i:=1 to n do g1:=g1+(StrToFloat(sg1.CelLs[1,i])-sx)*(StrToFloat(sg1.CelLs[1,i+1])-sx);
g1:=g1/(n-1);
g2:=0;for i:=1 to n do g2:=g2+(StrToFloat(sg1.CelLs[1,i])-sx)*(StrToFloat(sg1.CelLs[1,i+2])-sx);
g2:=g2/(n-2);
R1:=g1/s; R2:=g2/s; A1:=(R1-R1*R2)/(1-sqr(R1)); A2:=R2-A1*R1;
for i:=0  to k do
 begin
sg1.Cells[1,n+i+1]:=FloatToStrF(A1*(StrToFloat(sg1.CelLs[1,n+i])-sx)+A2*(StrToFloat(sg1.CelLs[1,n+i-1])-sx),ffFixed,12,2);
sg3.Cells[1,i]:=FloatToStrF((2+3*StrToFloat(sg1.Cells[1,n+i+1])+4*(n+i+1)), ffFixed,15,2);
sg4.Cells[1,i]:=FloatToStrF((a1+b1*(n+i+1)), ffFixed,15,3);
end;
 end;