Error dehydrating Property value for Entities.Mesa.Mesastatus

Question

I mapped the classes Mesa and Mesastatus with Fluent Nhibernate, according to the code below:

CLASS

 public class Mesa   
 {
    public virtual int MesaId { get; set; }
    public virtual int Numero { get; set; }
    public virtual int MesaStatusId { get; set; }
    public virtual decimal SubTotal { get; set; }
    public virtual decimal PorcentagemGorgeta { get; set; }
    public virtual decimal TotalGorgeta { get; set; }
    public virtual decimal Total { get; set; }
    public virtual MesaStatus MesaStatus { get; set; }
}

public class MesaStatus
{
    public virtual int MesaStatusId { get; set; }
    public virtual string Descricao { get; set; }
}

MAPPING

public class MesaMap : ClassMap<Mesa>
{
    public MesaMap()
    {
        Id(p => p.MesaId);
        Map(p => p.Numero).Not.Nullable();
        Map(p => p.MesaStatusId).Not.Nullable();
        Map(p => p.SubTotal).Not.Nullable();
        Map(p => p.PorcentagemGorgeta).Not.Nullable();
        Map(p => p.TotalGorgeta).Not.Nullable();
        Map(p => p.Total).Not.Nullable();

        References(x => x.MesaStatus).PropertyRef("MesaStatusId").ForeignKey("FK_Mesa_MesaStatus");
        Table("Mesa");
    }
}

public class MesaStatusMap : ClassMap<MesaStatus>  
{
        public MesaStatusMap()
        {
            Id(p => p.MesaStatusId);
            Map(p => p.Descricao).Length(40).Not.Nullable();
            Table("MesaStatus");
        }
}

When I try to insert the table class, I get the error "Error dehydrating Property value for Entities.Mesa.Mesastatus". How to Correctly Map Classes, to Be Able to Insert into the Database?