请教修改一段代码(100分)

以下代码在重复执行时会出现：　对象打开时，不允许操作的提示，不知何解？请各位指教！
procedure TForm58.Button2Click(Sender: TObject);
var
connstr:string;
begin
if OpenDialog1.Execute then
begin
connstr:='Provider=Microsoft.Jet.OLEDB.4.0;Data Source=';
connstr:=connstr+OpenDialog1.FileName;
connstr:=connstr+';Mode=Read;Extended Properties=Excel 8.0;Persist Security Info=False';
frmparame.ADOConnection1.ConnectionString:=connstr;
frmparame.ADOConnection1.Connected:=True;
frmparame.ADOConnection1.GetTableNames(ListBox1.Items,False);

procedure TForm58.Button2Click(Sender: TObject);
var
connstr:string;
begin
if OpenDialog1.Execute then
begin
connstr:='Provider=Microsoft.Jet.OLEDB.4.0;Data Source=';
connstr:=connstr+OpenDialog1.FileName;
connstr:=connstr+';Mode=Read;Extended Properties=Excel 8.0;Persist Security Info=False';
frmparame.ADOConnection1.Close; //加上这一句
frmparame.ADOConnection1.ConnectionString:=connstr;
try
frmparame.ADOConnection1.Connected:=True;
except
ShowMessage('连接数据库失败！');
Exit;
end;
frmparame.ADOConnection1.GetTableNames(ListBox1.Items,False);

多谢指教！