c# - Local sequence not supported on LINQ to SQL. So how can I do this query?

Question

That's my query:

var utenti = from User utente in db.User
             join amico in amiciParsed on new { utente.Nome, utente.Cognome } equals new { Nome = amico.first_name, Cognome = amico.last_name }
             select utente;

but I got that message:

Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator.

So how can I resolve the situation? Tried to store in a variable db.User, but nothing change.