该字符未被识别为有效的datatime

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace 更新数据表
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

    private void Form1_Load(object sender, EventArgs e)
    {
        string sql_str;
        string constr = "server=.;database=CJGL;integrated security=true";
        SqlConnection myconnection = new SqlConnection(constr);
        try
        {
            myconnection.Open();
            sql_str = "select 学号,姓名,性别,出生日期,专业,学分 from student";
            SqlDataAdapter mydataadapter = new SqlDataAdapter(sql_str,myconnection);
            DataSet mydataset = new DataSet();
            mydataadapter.Fill(mydataset,"student");
            DataRow dr = mydataset.Tables[0].NewRow();
            dr["学号"] = textBox1.Text;
            dr["姓名"] = textBox2.Text;
            dr["性别"] = textBox3.Text;
            dr["出生日期"] = textBox4.Text;
            dr["专业"] = textBox5.Text;
            dr["学分"] = textBox6.Text;
            SqlCommandBuilder scb = new SqlCommandBuilder(mydataadapter);
            mydataset.Tables[0].Rows.Add(dr);
            mydataadapter.Update(mydataset,"student");
        }
            catch(Exception ex)
        {
                MessageBox.Show(ex.Message.ToString());
            }
        finally
         {
            myconnection.Close();
         }

        }
    }
}
    ![图片说明](https://img-ask.csdn.net/upload/201605/08/1462699983_513763.png)

你应该把那几个textBox输入的内容贴出来啊，这样看代码是看不出问题的