NHibernate.HibernateException was unhandled
  Message="Could not create the driver from NHibernate.Driver.SqlServerCeDriver."
  Source="NHibernate"
  StackTrace:
       at NHibernate.Connection.ConnectionProvider.ConfigureDriver(IDictionary settings)
       at NHibernate.Connection.ConnectionProvider.Configure(IDictionary settings)
       at NHibernate.Connection.ConnectionProviderFactory.NewConnectionProvider(IDictionary settings)
       at NHibernate.Cfg.SettingsFactory.BuildSettings(IDictionary properties)
       at NHibernate.Cfg.Configuration.BuildSettings()
       at NHibernate.Cfg.Configuration.BuildSessionFactory()

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <!--  an ISessionFactory instance -->
  <session-factory>
    <!--   properties  -->
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlServerCeDriver</property>
    <property name="connection.connection_string">Data Source ='C:\Temp\SimpleDB.sdf'; Password='simple'</property>
    <property name="show_sql">false</property>
    <property name="dialect">NHibernate.Dialect.MsSqlCeDialect</property>
    <property name="use_outer_join">true</property>
    <!--   mapping files  -->
    <mapping assembly="MyNHib" />
  </session-factory>
</hibernate-configuration>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyNHib" namespace="MyNHib">
<class name="MyNHib.User" table="users">
<id name="Id" column="LogonId" type="String" length="20">
  <generator class="assigned" />
  </id>
  <property name="UserName" column="Name" type="String" length="40" />
  <property name="Password" type="String" length="20" />
  <property name="EmailAddress" type="String" length="40" />
  <property name="LastLogon" type="DateTime" />
  </class>
  </hibernate-mapping>

....
ISessionFactory session =
   new Configuration().Configure().BuildSessionFactory();

   ISession sess = session.OpenSession();
   User usr = new User();
   usr.Id = "1";
         usr.UserName = "Name";
         usr.Password = "Pssw";
         usr.EmailAddress = "e@mail";
         usr.LastLogon = DateTime.Now;

         sess.Save(usr);
         sess.Flush();
         sess.Close();
...