添加学生信息后添加该学生登陆信息出错，这是为什么？

try
            {
                string sqll = "insert into Student(Sno,Sname,Ssex,Sdept,Sage) values ('"+stu_sno.Text.Trim ()+"','"+stu_sname.Text .Trim ()
                    +"','"+stu_sex.Text .Trim ()+"','"+stu_dept.Text.Trim()+"',"+int.Parse (stu_age.Text.Trim())+")";
                //插入前检查该学生信息是否已经存在
                //存在该学生，信息无法插入
                conn = new OleDbConnection(myconn);
                conn.Open();
                cmd = new OleDbCommand("select * from Student where Sno = '"+stu_sno.Text.Trim ()+"'",conn);
                read = cmd.ExecuteReader();
                if (read.Read()) //存在该学生
                {
                    MessageBox.Show("该学生信息存在，添加无效!");
                }
                else  //添加学生信息
                {
                    cmd = new OleDbCommand(sqll, conn);
                    cmd.ExecuteNonQuery();//学生信息添加

                    //添加该生注册信息，在Student_Login表中插入数据，学号，和密码（默认为111）
                    string pwd = "111";
                    string ssql = "insert into Student_Login(Sno,Password) values ('" + stu_sno.Text.Trim() + "','" + pwd + "')";
                    OleDbCommand cc = new OleDbCommand(ssql,conn);
                    cc.ExecuteNonQuery();
                    
                }
            }
            catch (Exception ee)
            {
                MessageBox.Show(ee.ToString());
            }
            finally
            {
                read.Close();
                conn.Close();  //关闭数据库连接

            }