输入字符串格式不正确

string teacherid = (string)Session["teacharid"];
DAL.Sjtm dal = new DAL.Sjtm();
Model.Sjtm model = new Model.Sjtm();

    model.TeacherId = teacherid;
    model.TmName = TextBox1.Text;
    model.TmType = DropDownList1.SelectedValue;
    model.年度1 = DateTime.Now.Year.ToString();
    model.State = 0;
    dal.Add(model);![图片说明](https://img-ask.csdn.net/upload/201711/12/1510481360_729657.png)

model.TeacherId = teacherid;
model.TmType = DropDownList1.SelectedValue;
这两个左右等号两边类型是否匹配