org.hibernate.MappingException: Could not determine type for: java.util.Set, for columns: [org.hibernate.mapping.Column(accountParties)]
        at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:266)
        at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:253)
        at org.hibernate.mapping.Property.isValid(Property.java:185)
        at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:440)
        at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
        at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
        at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
        at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:713)

@Entity
public class Account implements Serializable {
    ...
    private Set<AccountParty> accountParties =
        new HashSet<AccountParty>();

    @CollectionOfElements(targetElement = AccountParty.class)
    @JoinTable(name="Account_AccountParties")
    public Set<AccountParty> getAccountParties() {
        return accountParties;
    }

    public void setAccountParties(Set<AccountParty> accountParties) {
        this.accountParties = accountParties;
    }
}

@Embeddable
public class AccountParty implements Serializable {
    private Party party;

    @ManyToOne(targetEntity=Party.class)
    public Party getParty() {
        return party;
    }

    public void setParty(Party party) {
        this.party = party;
    }
}