trace of error in sqlalchemy

trace.py

 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 115, in __init__
  2 self._set_entities(entities)
  3 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 124, in _set_entities
  4 self._set_entity_selectables(self._entities)
  5 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 157, in _set_entity_selectables
  6 ent.setup_entity(*d[entity])
  7 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2861, in setup_entity
  8 self._with_polymorphic = ext_info.with_polymorphic_mappers
  9 File "/project/s/lib/python2.6/site-packages/sqlalchemy/util/langhelpers.py", line 612, in __get__
 10 obj.__dict__[self.__name__] = result = self.fget(obj)
 11 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/mapper.py", line 1458, in _with_polymorphic_mappers
 12 configure_mappers()
 13 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/mapper.py", line 2153, in configure_mappers
 14 mapper._post_configure_properties()
 15 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/mapper.py", line 1275, in _post_configure_properties
 16 prop.init()
 17 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/interfaces.py", line 231, in init
 18 self.do_init()
 19 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/properties.py", line 1027, in do_init
 20 self._process_dependent_arguments()
 21 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/properties.py", line 1082, in _process_dependent_arguments
 22 self.target = self.mapper.mapped_table
 23 File "/project/s/lib/python2.6/site-packages/sqlalchemy/util/langhelpers.py", line 612, in __get__
 24 obj.__dict__[self.__name__] = result = self.fget(obj)
 25 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/properties.py", line 1009, in mapper
 26 configure=False)
 27 File "/project/s/lib/python2.6/site-packages/sqlalchemy/orm/util.py", line 1122, in class_mapper
 28 "Class object expected, got '%r'." % class_)
 29 ArgumentError: Class object expected, got 'Table('Users', MetaData(bind=None), Column('UserID', BigInteger(), table=<Users>, primary_key=True, nullable=False), Column('UserType', Enum('UI', 'VC', 'API    '), table=<Users>, nullable=False, default=ColumnDefault('UI')), Column('Email', String(length=50), table=<Users>, default=ColumnDefault('')), Column('FirstName', String(length=50), table=<Users>, def    ault=ColumnDefault('')), Column('LastName', String(length=50), table=<Users>, default=ColumnDefault('')), Column('ContactID', Integer(), ForeignKey('Contacts.ContactID'), table=<Users>), Column('Compa    nyID', Integer(), ForeignKey('Companies.CompanyID'), table=<Users>), Column('Locale', String(length=10), table=<Users>), Column('Superuser', Boolean(), table=<Users>, default=ColumnDefault(False)), Co    lumn('SuperCompanyMember', Boolean(), table=<Users>, default=ColumnDefault(False)), Column('Suspended', Boolean(), table=<Users>, default=ColumnDefault(False)), Column('Timezone', String(length=100),     table=<Users>, default=ColumnDefault('UTC')), Column('Secret', String(length=128), table=<Users>), Column('MD5Password', String(length=250), table=<Users>), schema=None)'.