The ConnectionString property has not been initialized

[federrer]

"property کانکشن استرینگ ،مقدار دهی اولیه نشده است-
The ConnectionString property has not been initialized." !!!

کدفایل web.config:

<connectionStrings>
<remove name="LocalSqlServer" />
<add name="LocalSqlServer" connectionString="data source=.\SQLEXPRESS;Integrated Security=true;AttachDBFilename=C:\INETPUB\WWWROOT\ BANK.MDF;User Instance=True"
providerName="System.Data.SqlClient" />
<add name="MainConnStr" connectionString="data source=.\SQLEXPRESS;Integrated Security=true;AttachDBFilename=C:\INETPUB\WWWROOT\ BANK.MDF;User Instance=true"
providerName="System.Data.SqlClient" />
</connectionStrings>
<system.web>
<compilation debug="true"/>
<authentication mode="Windows"/> </system.web>

و این کد رو هم تو صفحه نوشته ام که میخوام کانکشن رو باز کنم و پارامترها رو واسه یه استورپروسیجر بفرستم:


string CS = (string)ConfigurationManager.AppSettings["MainConnStr"];
SqlConnection Cnn= new SqlConnection(CS);

SqlCommand A = new SqlCommand("spRegister",Cnn);
()A.CommandType = CommandType.StoredProcedure;
A.Connection=Cnn;

string findmadrak = DDL1.SelectedItem.Text.ToString();
string findsanavat = DDL2.SelectedItem.Text.ToString();

A.Parameters.Add(newSqlParameter("@MADRAK", SqlDbType.NVarChar));
A.Parameters["@MADRAK"].Value = findmadrak;
A.Parameters.Add(newSqlParameter("@SANAVAT", SqlDbType.NVarChar));
A.Parameters["@SANAVAT"].Value = findsanavat;

A.Connection.Open();
A.ExecuteNonQuery();
A.Connection.Close();



A.Connection.Open(); گیر میده که :


Exception Details: System.InvalidOperationException: The ConnectionString property has not been initialized.

[fakhravari]

SqlConnection con = new SqlConnection(WebConfigurationManager.ConnectionSt rings["DBCenter"].ToString());

public void AddRecord()
{
try
{

SqlCommand cmd = new SqlCommand("News_Add", con);
cmd.CommandType = CommandType.StoredProcedure;
con.Open();

cmd.Parameters.Add("@Title", SqlDbType.NVarChar).Value = Title;
cmd.Parameters.Add("@Abstract", SqlDbType.NVarChar).Value = Abstract;
cmd.Parameters.Add("@Contents", SqlDbType.NVarChar).Value = Contents;
cmd.Parameters.Add("@AddDate", SqlDbType.NVarChar).Value = AddDate;
cmd.Parameters.Add("@img", SqlDbType.NVarChar).Value = photoFilePath;
cmd.ExecuteNonQuery();
con.Close();
}
catch
{
lasteror = "اشکال در ثبت اطلاعات";
}
}