asp.net插入记录问题

向数据库中插入一条记录，一直插不成功。代码如下：
string strCourseId = tbCourseID.Text;
        string strClassName = droplistClassName.SelectedValue;
        string strSubjectName = droplistSubjectName.SelectedValue;
        string strTeacherName = droplistTeacherName.SelectedValue;
        string strBeginDate = tbBeginDate.Text;
        string strFinishDate = tbFinishDate.Text;
        string strRe = tbRe.Text;
        int iCourseId = int.Parse(strCourseId);
        DateTime date1 = DateTime.Parse(strBeginDate);
        DateTime date2 = DateTime.Parse(strFinishDate);
        string sql = "insert into Course(CourseID,ClassName,SubjectName,TeacherName,BeginDate,FinishDate,Re) values('" + iCourseId + "','" + strClassName + "','" + strSubjectName + "','" + strTeacherName + "','" + date1   + "','" +date2 + "','" + strRe + "')";
        SQLServer db = new SQLServer();
        int State = db.AddInfo(sql);
        if (State == 1)
        {
            Response.Write("添加成功!");
        }
        else
        {
            Response.Write("添加失败！");
        }
其中AddInfo的方法的代码如下：
 public int AddInfo(string sql)
    {
        int state;
        SqlConnection conn = new SqlConnection();
        conn.ConnectionString = connstring;
        SqlCommand comm = new SqlCommand(sql,conn);
        try
        {
            conn.Open();
            comm.ExecuteNonQuery();
            conn.Close();
            state = 1;
        }
        catch
        {
            state = 0;
            conn.Close();
        }
        return state;
    }
请各位帮忙看看，到底哪里出错了。谢谢啊。