public class Uspd
{
public virtual int cd_id{get;set;}
public virtual string description{get;set;}
public virtual IList<Meter> meter { get; set; }
}

public class Meter
{
public virtual int pm_id{get;set;}
public virtual Uspd cd_id{get;set;}
public virtual string description {get;set;}
public virtual IList<Events> events { get; set; }
}

public class Event
{
public virtual int ev_id{get;set;}
public virtual Meter ev_pm_id {get;set;}
public virtual Uspd ev_cd_id {get;set;}
public virtual string Description {get;set;}
}

public class UspdMap
{
Id(x => x.cd_id, "\"cd_id\"").Not.Nullable();
Map(x => x.description, "\"description\"");
HasMany(x => x.meter).KeyColumns.Add("pm_Id").Inverse().Cascade.All();
}

public class MeterMap
{
CompositeId().KeyProperty(x => x.pm_id, "\"pm_Id\"").KeyReference(x => x.cd_id, "\"cd_id\"");
Map(x => x.description, "\"description\"");
HasMany(x => x.events).KeyColumn("ev_pm_id").KeyColumn("ev_cd_id").Inverse().Cascade.All();
}

public class Event
{
Id(x => x.EV_ID).Not.Nullable().GeneratedBy.Increment();
References(x => x.EV_CD_ID).Column("EV_CD_ID").Cascade.All();
HasOne(x => x.EV_PM_ID).PropertyRef("pm_Id").PropertyRef("cd_id").Cascade.All(); [color=red]<- мне кажется тут я не правильно что то написал[/color]
Map(x => x.description, "\"description\"");
}

collection foreign key mapping has wrong number of columns: Meter.Events type: component[pm_Id,cd_id]