ProjectPract6P.exe raised exception class econverterror with message'''isnot a valid floating point value-C++ Buider 6.0

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
 
#include "Pract6.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
        int n = 3; 
        double **a, *b;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
 
 
void __fastcall TForm1::FormCreate(TObject *Sender)
{
        Edit1->Text=IntToStr(n); 
        StringGrid1->ColCount = n+1;
        StringGrid1->RowCount = n+1;
        StringGrid2->RowCount = n+1;
        StringGrid3->RowCount = n+1;
 
        StringGrid1->Cells[0][0] = "Mass A";
        StringGrid2->Cells[0][0] = "Mass B";
        StringGrid3->Cells[0][0] = "Mass Y"; 
        for(int i=1; i<=n;i++){ 
                StringGrid1->Cells[0][i]="i="+IntToStr(i); 
                StringGrid1->Cells[i][0]="j="+IntToStr(i); 
        } 
 
 
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Edit1Change(TObject *Sender)
{
        int i; 
        n=StrToInt(Edit1->Text); 
        StringGrid1->ColCount = n+1;        StringGrid1->RowCount = n+1; 
        StringGrid2->RowCount = n+1;       StringGrid3->RowCount = n+1; 
        for(i=1; i<=n;i++){ 
                StringGrid1->Cells[0][i]="i="+IntToStr(i); 
                StringGrid1->Cells[i][0]="j="+IntToStr(i); 
        }         
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
        double s; 
        int i,j; 
        a = new double*[n];
        for(i=0; i<n;i++)  a[i] = new double[n];
        b = new double[n];
     for(i=0; i<n;i++)
     {
      for(j=0; j<n;j++)   a[i][j]=StrToFloat(StringGrid1->Cells[j+1][i+1]);
      b[i]=StrToFloat(StringGrid2->Cells[0][i+1]);
     }
 
     for(i=0; i< n;i++)
      {
      for(s=0, j=0; j<n;j++)  s += a[i][j]*b[j];
      StringGrid3->Cells[0][i+1] =  FloatToStrF(s, ffFixed,8,2);
      }
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button2Click(TObject *Sender)
{
      for(int i=0; i<n;i++) delete []a[i]; 
      delete []a;        delete []b; 
      ShowMessage("Ram free!"); 
      Close();
}
//---------------------------------------------------------------------------