django postgreSQL连接问题

我在连接Django中的PostgreSql时遇到了问题

>>python manage.py shell
>>> from django.db import connection
>>> cursor = connection.cursor()
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 250, in cursor
    cursor = self.make_debug_cursor(self._cursor())
  File "/usr/local/lib/python2.6/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 148, in _cursor
    cursor.execute("SET TIME ZONE %s", [settings_dict['TIME_ZONE']])
DataError: unrecognized time zone name: "America/Chicago"

但是，当我尝试

>>> c=connection.cursor()
>>> c

>>> c.execute("select * from test")
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/local/lib/python2.6/dist-packages/django/db/backends/util.py", line 34, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.6/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute
    return self.cursor.execute(query, args)
DatabaseError: current transaction is aborted, commands ignored until end of transaction block

>>> connection.commit()
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 202, in commit
    self.set_clean()
  File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 147, in set_clean
    raise TransactionManagementError("This code isn't under transaction management")
TransactionManagementError: This code isn't under transaction management
>>> c.execute("select * from test")
>>> c.fetchone()
(1, 100, u'abd')

我不知道问题出在哪里
我做谷歌但没有帮助，任何人都可以帮忙吗？非常感谢 .
我的设置是：

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2', # Add 'postgresql_psycopg2', 'postgresql', 'mysql', 'sqlite3' or 'oracle'.
        'NAME': 'mydb',                      # Or path to database file if using sqlite3.
        'USER': 'postgres',                      # Not used with sqlite3.
        'PASSWORD': '123',                  # Not used with sqlite3.
        'HOST': '/tmp',                      # Set to empty string for localhost. Not used with sqlite3.
        'PORT': '5432',                      # Set to empty string for default. Not used with sqlite3.
        #'OPTIONS':True,
    }
}