从网上搜说是sql语句有错误，但是感觉应该没有错误

           代码如下
           protected void Button1_Click(object sender, EventArgs e)
   {
       SqlConnection cn = new SqlConnection();
       cn.ConnectionString = ConfigurationManager.ConnectionStrings["connectname"].ConnectionString;
       cn.Open();
       SqlCommand cm = new SqlCommand("insert into student(id,name,num,time,ctime) values('" + this.TextBox1.Text+ "', '" + this.TextBox2.Text + "', '" + this.TextBox3.Text + "', '" + this.TextBox4.Text + "', '" + this.TextBox5.Text+"'",cn);
       cm.ExecuteNonQuery();//这个地方报错
       cn.Close();

求大神解救！！！！