provider name is not found,what should I do?

here is my web.config code<configuration> <connectionstrings> <add name="ConnectionString" providername="System.Data.SqlClient" connectionstring="Data Source=.;Initial Catalog=sampleDB;Integrated Security=True;Pooling=False">"

<system.data> <dbproviderfactories> <add description=".Net Framework Data Provider for SqlServer" type="System.Data.SqlClient.SqlClientFactory, System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" name="Sql Client DataProvider" invaiant="System.Data.SqlClient">

<system.web> <compilation targetframework="4.0" debug="true">

and here is my configuration.cs code:
namespace SConfiguration
{
public class Configuration
{

private static string dbConnectrionString;
private static string dbProviderName;
public Configuration()
{
dbConnectrionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
dbProviderName = ConfigurationManager.ConnectionStrings["ConnectionString"].ProviderName;

}
public static string DBConnectionString
{
get { return dbConnectrionString; }
}
public static string DBProviderName
{
get { return dbProviderName; }
}

}

here is my genericData.cs class:
public class GenericData
{
public GenericData()
{
}
public static DataTable ExecuteReader(DbCommand Command)
{
DataTable table;
try
{
Command.Connection.Open();
DbDataReader reader = Command.ExecuteReader();
table = new DataTable();
table.Load(reader);
}
catch (Exception ex)
{ throw ex; }
finally
{ Command.Connection.Close(); }
return table;
}

public static DbCommand CreateCommand()
{
string dbProviderName = Configuration.DBProviderName;
string dbConnectionString = Configuration.DBConnectionString;
DbProviderFactory factory = DbProviderFactories.GetFactory(dbProviderName);
DbConnection Connection = factory.CreateConnection();
Connection.ConnectionString = dbConnectionString;
DbCommand command = Connection.CreateCommand();
command.CommandType = CommandType.StoredProcedure;
return command;
}