IAutoMappingOverride not calling

I have AutoMapping Setup. But my IAutoMappingOverride method not firing. But if call .Override it work fine. It is a many to many relationship.
Tables (Resource, Role, Permission)
Classes (Resource and Role)

        return Fluently.Configure()
            .Database(MsSqlConfiguration.MsSql2008
            .ConnectionString("server=.\\SQLEXPRESS;database=Fasttrak3;Integrated Security=SSPI"))
            .Mappings(m => m.AutoMappings
                .Add(
                    AutoMap.AssemblyOf<Program>()
                    .Setup(s => s.FindIdentity =
                        property => property.Name == property.DeclaringType.Name + "Id")
                    .Conventions.Setup(i =>
                    {
                        i.Add<PrimaryKeyConvention>();
                        i.Add<CustomForeignKeyConvention>();
                    }
                        )
                .UseOverridesFromAssemblyOf<RoleMappingOverride>()
                ))
            .BuildSessionFactory();

// Override code

    public class RoleMappingOverride : IAutoMappingOverride<Resource>
    {
        public void Override(AutoMapping<Resource> mapping)
        {
            mapping.HasManyToMany(x => x.Roles).Cascade.All().Table("Permission");
        }
    }

I don't have ResourceMap mapping information anywhere. Is it really necessary before calling override?