关于 至少一个参数没被赋数值!!!!

到底哪个值没赋值啊,求求各位高手帮我解决一下:

//实体类实例化

Items item = new Items();

item.excID = get_excID() + 1;

item.excTypeID = this.lBType_main.SelectedValue.ToString();

item.excTypeSonID = this.lBType_son.SelectedValue.ToString();

item.excItemTitle = this.txtGoodName.Text;

item.excItemDescription = this.txtGoodDesription.Text;

item.excNewOld = this.ddlNewLevel.SelectedValue.ToString();

item.excGoodNum =this.txtGoodNum.Text;

item.excItemAddMan = excAddMan;

//插入语句

OleDbConnection conn = DBConn.createConn();

conn.Open();

OleDbCommand cmd = new OleDbCommand("insert into exchanges values(@excID,@excTypeID,@excTypeSonID,@excItemTitle,@excItemAddMan,@excItemDescription,@excGoodNum,@excNewOld)", conn);

OleDbParameter para = new OleDbParameter("@excID", OleDbType.Numeric);

para.Value = item.excID;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excTypeID", OleDbType.Numeric);

para.Value = item.excTypeID;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excTypeSonID", OleDbType.Numeric);

para.Value = item.excTypeSonID;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excItemTitle", OleDbType.VarChar, 50);

para.Value = item.excItemTitle;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excItemAddMan", OleDbType.VarChar, 50);

para.Value = item.excItemAddMan;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excItemDescription", OleDbType.VarChar, 100);

para.Value = item.excItemDescription;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excGoodNum", OleDbType.Numeric);

para.Value = item.excGoodNum;

cmd.Parameters.Add(para);

para = new OleDbParameter("@excNewOld", OleDbType.VarChar, 50);

para.Value = item.excNewOld;

cmd.ExecuteNonQuery();

在使用存储过程的时候，参数没有给指定值，或是值不合法