ConnectionString 属性尚未初始化

[百思软件工作室]

请问这是怎么回事啊
在！ispostback中绑定时,不会出现错误
但是在删除等事件后在ispostback绑定时,出现了ConnectionString 属性尚未初始化的错误
行 141: catch(Exception ee)
行 142: {
行 143: throw ee;
行 144: }
行 145: finally



<appSettings>
<add key="sqlconn" value="server=.;database=disney;uid=newart;pwd=newart@2008com"/>
<add key ="picbig" value ="3072"/>
<add key ="pictype" value=".jpeg,.jpg,.png,.gif,.pdf,.bmp"/>
</appSettings>
<connectionStrings>
</connectionStrings>


private SqlConnection conn = null;
private SqlCommand cmd;
private SqlDataAdapter da;
private SqlDataReader dr;
private DataSet ds;
public string sqlconn;



public SQLHelper()
{
sqlconn = ConfigurationManager.AppSettings["sqlconn"].ToString();

}



public DataTable bindtable(string info)
{
try
{
Open();
da = new SqlDataAdapter(info,conn);
ds = new DataSet();
da.Fill(ds);

}
catch(Exception ee)
{
throw ee;
}
finally
{
Close();
}
return ds.Tables[0];


}

[sxu_nono]

conn=new SqlConnection(sqlconn);

[pgameli]

  public DataTable bindtable(string info)
        {
            try
            {
conn=new SqlConnection(sqlconn);
                conn.Open();
                da = new SqlDataAdapter(info,conn);
                ds = new DataSet();
                da.Fill(ds);

            }
            catch(Exception ee)
            {
                throw ee;
            }
            finally
            {
                Close();
            }
            return ds.Tables[0];

       
        }