I've been writing a small address database, and using a TAutoInc field to keep track of an entry.  The problem comes when I try and update the the field I get an error "Field 'ContactNo' is not indexed and cannot be modified"  Can anyone shed some light on this.  Thanks...

type
  TPersonalIndexRecord = class(TObject)
    Value : string;
    Index : Longint;
  end;

procedure TDataModule2.SetIndexToCurrent;

var CurrentRec : TPersonalIndexRecord;
    CurrentIndex : Longint;
    Success : boolean;

begin
  with Table1 do
    begin
      SetKey;
      CurrentRec := PersonalIndexList.Items[Main.ListBox1.ItemIndex];
      CurrentIndex := CurrentRec.Index;
      FieldByName('ContactNo').AsVariant := CurrentIndex;
      Success := Gotokey;
    end;
end;