解决了一个问题，又来一个，高手快来帮我看看，很急啊！！！！！！！！！！！！！！！！！！！！！！！

//登录效验
        private void button1_Click(object sender, EventArgs e)
        {
            string str;
            int n;
            DataSet ds = new DataSet();
            OleDbDataAdapter da;
            str = "select `user`,`pws`,`role` from `user` where `user`='" + comboBox1.Text + "'";
            //MessageBox.Show(str);
            try
            {
                da = new System.Data.OleDb.OleDbDataAdapter(str, oleDbConnection1);
                da.Fill(ds);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            //ds.Tables[0].Rows[0][1];   
            try
            {
                Form1.info.user = ds.Tables[0].Rows[0][0].ToString();
                Form1.info.pws = ds.Tables[0].Rows[0][1].ToString();
                Form1.info.role = ds.Tables[0].Rows[0][2].ToString();
                //MessageBox.Show(Form1.info.user + Form1.info.pws + Form1.info.role);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            n = 0;
            try
            {
                if ((textBox1.Text.CompareTo(Form1.info.role)) > 0)
                {//登录成功
                    Form1 f1 = new Form1();
                    this.Hide();
                    f1.Show();                }
                else
                {//登录失败三次，退出系统
                    n++;
                    if (n >= 3)
                    {
                        MessageBox.Show("登录失败超过三次，系统自动退出！", "登录信息", MessageBoxButtons.OK, MessageBoxIcon.Error);
                        this.Close();
                    }
                    else
                    {
                        MessageBox.Show("用户不存在或密码错误！", "登录信息", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        textBox1.Text = "";
                        textBox1.Focus();
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
错误信息是：问题很严重，程序要关闭