Fejl ved oprettelse af forbindelse til database

Når jeg forsøger at oprette en forbindelse til MS Sql til NHibernate, så får jeg følgende fejl:
cannot open connection ---> System.Data.SqlClient.SqlException: A connection was successfully established with the server, but then an error occurred during the login process. (provider: Named Pipes Provider, error: 0 - No process is on the other end of the pipe.)

Hvad skyldes dette?

Her er min 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" />
    </configSections>

    <nhibernate>
        <add key="hibernate.connection.provider" value="NHibernate.Connection.DriverConnectionProvider" />
        <add key="hibernate.dialect" value="NHibernate.Dialect.MsSql2000Dialect" />
        <add key="hibernate.connection.driver_class" value="NHibernate.Driver.SqlClientDriver" />
        <add key="hibernate.connection.connection_string" value="Server=127.0.0.1;initial catalog=mydatabase;Integrated Security=SSPI" />
    </nhibernate>

</configuration>