Conexão com SQL Server - Falha de logon do usuário

Meu hibernate.cfg.xml:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration
xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="dialect">NHibernate.Dialect.MsSql2012Dialect</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">
      Server=(local);Database=TesteDeConexao;User Id=root;Password=1234;
    </property>
    <property name="show_sql">true</property>
  </session-factory>
</hibernate-configuration>

Mensagem de erro:

NHibernate.HibernateException: 'Falha de logon do usuário 'root'.'

O que poderia ser?