Nhibernate

estou inciando com o nhibernate e estou empacado em um erro se alguem puder me ajudar

namespace NHTOOLS
{
public class NHibernateHelper
{

 private const string CurrentSessionKey = "nhibernate";

 private static NHibernate.Cfg.Configuration config;

 private static readonly ISessionFactory sessionFactory;

 static NHibernateHelper()
 {

 config = new NHibernate.Cfg.Configuration();

 sessionFactory = config.BuildSessionFactory();--> aqui nesta linha da o erro

 sessionFactory = config.Configure().BuildSessionFactory();

 }

 public static ISession GetCurrentSession()
 {

 CloseSession();

 HttpContext context = HttpContext.Current;

 ISession currentSession = context.Items[CurrentSessionKey] as ISession;

 if (currentSession == null)
 {

 currentSession = sessionFactory.OpenSession();

 context.Items[CurrentSessionKey] = currentSession;

 }

 return currentSession;

 }

 public static void CloseSession()
 {

 HttpContext context = HttpContext.Current;

 ISession currentSession = context.Items[CurrentSessionKey] as ISession;

 if (currentSession == null)
 {

 // No current session

 return;

 }

 currentSession.Close();

 context.Items.Remove(CurrentSessionKey);

 }

 public static void CloseSessionFactory()
 {

 if (sessionFactory != null)
 {

 sessionFactory.Close();

 }

 }
 }
}

APP.Config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
	<configSections>
 <section name="nhibernate" type="System.Configuration.NameValueSectionHandler, System, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
 <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
	</configSections>

	<nhibernate>
 <add key="hibernate.connection.provider" value="NHibernate.Connection.DriverConnectionProvider"/>
 <add key="hibernate.dialect" value="NHibernate.Dialect.FirebirdDialect"/>
 <add key="hibernate.connection.driver_class" value="NHibernate.Driver.FirebirdClientDriver"/>
 <add key="hibernate.connection.connection_string" value="User=SYSDBA;Password=masterkey;Database=D:\vs2008\Agenda\SLAGENDA\BD\AG.FDB;Dialect=3;ServerType=1;"
 />
	</nhibernate>

	<log4net debug="false">

 <!-- Define some output appenders -->
 <appender name="trace"
 type="log4net.Appender.TraceAppender, log4net">
 <layout type="log4net.Layout.PatternLayout,log4net">
 <param name="ConversionPattern"
 value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
 </layout>
 </appender>

 <appender name="console"
 type="log4net.Appender.ConsoleAppender, log4net">
 <layout type="log4net.Layout.PatternLayout,log4net">
 <param name="ConversionPattern"
 value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
 </layout>
 </appender>

 <appender name="rollingFile"
 type="log4net.Appender.RollingFileAppender,log4net" >

 <param name="File" value="h:\log.txt" />
 <param name="AppendToFile" value="false" />
 <param name="RollingStyle" value="Date" />
 <param name="DatePattern" value="yyyy.MM.dd" />
 <param name="StaticLogFileName" value="true" />

 <layout type="log4net.Layout.PatternLayout,log4net">
 <param name="ConversionPattern"
 value="%d [%t] %-5p %c - %m%n" />
 </layout>
 </appender>

 <!-- Setup the root category, add the appenders and set the default priority -->
 <root>
 <priority value="DEBUG" />
 <appender-ref ref="console" />
 </root>

 <logger name="NHibernate">
 <level value="DEBUG" />
 </logger>

	</log4net>

	<runtime>
 <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
 <qualifyAssembly partialName="FirebirdSql.Data.FirebirdClient"
 fullName="FirebirdSql.Data.FirebirdClient, Version=2.5.2.0, Culture=neutral, PublicKeyToken=3750abcc3150b00c" />
 </assemblyBinding>
	</runtime>
</configuration>

nhibernate.cfg.xml

<?xml version="1.0" encoding="utf-8" ?>
<!-- To work with FireBird you must add the assembly binding for FirebirdClient ADO.NET 2.0 DataProvider
to your App.config.
Example:

<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
	<qualifyAssembly partialName="FirebirdSql.Data.FirebirdClient" fullName="FirebirdSql.Data.FirebirdClient, Version=2.0.1.0, Culture=neutral, PublicKeyToken=3750abcc3150b00c" />
</assemblyBinding>
</runtime>

 --><!--

This template was written to work with NHibernate.Test.
Copy the template to your NHibernate.Test project folder and rename it in hibernate.cfg.xml and change it
for your own use before compile tests in VisualStudio.

-->

<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
 <session-factory name="nhibernate">
 <property name="connection.driver_class">NHibernate.Driver.FirebirdClientDriver</property>
 <property name="connection.connection_string">Server=localhost; Database=D:\vs2008\Agenda\SLAGENDA\BD\AG.fdb; User=SYSDBA;Password=masterkey</property>
 <property name="show_sql">false</property>
 <property name="dialect">NHibernate.Dialect.FirebirdDialect</property>
 <property name="command_timeout">60</property>
 <property name="query.substitutions">true 1, false 0, yes 1, no 0</property>
 <property name="proxyfactory.factory_class">NHibernate.ByteCode.LinFu.ProxyFactoryFactory, NHibernate.ByteCode.LinFu</property>
	</session-factory>
</hibernate-configuration>