title: LinqToSQL Error : Operation is not valid due to the current state of the object
body: <p>During an update command I received the following error:</p>
  
  <blockquote>
    <p>Operation is not valid due to the current state of the object</p>
  </blockquote>
  
  <p>I tried to remove one column from the update command and it works fine.
  This column is a FK that is similar to the other FK that works fine.</p>
  
  <p>This is the code that executes the update:</p>
  
  <pre><code>                ti.NumeroTitolo = titolo.Numero;
                  ti.RKTipoTitoloGenereTitolo = titolo.RkTipoTitoloGenereTitolo;
                  ti.RKBanca = titolo.RkBanca;
                  ti.DataScadenza = titolo.DataScadenza;
                  ti.RKTipoEsito = titolo.RkTipoEsito; 
                  ti.ImportoTitolo = titolo.ImportoTitolo;
  
                  _dc.SubmitChanges();
  </code></pre>