python – TurboGears: sqlalchemy.exc.ArgumentError in admin crud

If I will use the automatic crud for the admin section, sometimes, when I try to create/edit some object I have the following error:

sqlalchemy.exc.ArgumentError: Class object expected, got '<bound method _class_resolver._resolve_name of <sqlalchemy.ext.declarative.clsregistry._class_resolver object at 0x7f2aba659860>>'.

For example, if I try to edit (or create) ad I have the following model:

class User(DeclarativeBase):
    __tablename__ = 'tg_user'

    user_id = Column(Integer, autoincrement=True, primary_key=True)
    user_name = Column(Unicode(16), unique=True, nullable=False)
    email_address = Column(Unicode(255), unique=True, nullable=False)
    display_name = Column(Unicode(255))
    _password = Column('password', Unicode(128))
    created = Column(DateTime, default=datetime.now)

    tg_player_id = Column(Integer, ForeignKey('player.player_id'))
    player = relationship("Player", backref='tg_user')


class Player(DeclarativeBase):

    __tablename__ = 'player'

    player_id = Column(Integer, primary_key=True, nullable=False)
    player_tg_id = Column(Unicode(30))
    username = Column(Unicode(100))