Error Message,"Invalid Floating point operation"?

procedure TfrmCheckPrime.Button1Click(Sender: TObject);
var
    myPrime:Extended;
    icount,i:LongInt;
begin
      icount:=0;
      myPrime :=StrToFloat(Edit1.Text);
      for i:= 2 to Trunc(myPrime-1) do
      begin
              if (Trunc(myPrime) mod I) = 0  then icount := icount + 1;
      end;

      if icount=0 then ShowMessage('This is prime number')
      else ShowMessage('This is not prime number');
end;

[Question]: When the text of the Edit1 is 4294967296. This number
Power(2,32). After i click the button, there is an Error Message,
                  "Invalid Floating point operation",and the extended is
the maximum declaration. Is there any way to solve this problem?