[求助]用OleDb对象更新数据库时出错了

<%@page language="C#"%>
<%@import namespace="System.Data"%>
<%@import namespace="System.Data.OleDb"%>
<script runat="server" language="c#">
void Page_Load(Object sender,EventArgs e)
{
OleDbConnection conn=new OleDbConnection();
conn.ConnectionString="Provider=Microsoft.jet.OLEDB.4.0;"+"Data Source="+Server.MapPath("mydatabase.mdb");
conn.Open();
string sql="UPDATE grade SET 数学=100 WHERE 学号 = '12'";
OleDbCommand comm=new OleDbCommand(sql,conn);
comm.ExecuteNonQuery();

string sql2="select * from grade";
comm.CommandText=sql2;
OleDbDataReader dr=comm.ExecuteReader();
dg.DataSource=dr;
dg.DataBind();
conn.Close();
}
</script>
<asp:DataGrid id="dg" runat="server"/>

高手帮忙,错在哪里??