TurboGears:TypeError: decoding Unicode is not supported

在turbogears的20分钟WIKI里面添加用户的时候
500 Internal error

The server encountered an unexpected condition which prevented it from fulfilling the request.

Page handler: <bound method Users.add of <tutorial.controllers.Users instance at 0xb72aabac>>
Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/CherryPy-2.2.1-py2.4.egg/cherrypy/_cphttptools.py", line 105, in _run
    self.main()
  File "/usr/lib/python2.4/site-packages/CherryPy-2.2.1-py2.4.egg/cherrypy/_cphttptools.py", line 254, in main
    body = page_handler(*virtual_path, **self.params)
  File "<string>", line 3, in add
  File "/usr/lib/python2.4/site-packages/TurboGears-1.0b1-py2.4.egg/turbogears/controllers.py", line 326, in expose
    output = database.run_with_transaction(
  File "<string>", line 5, in run_with_transaction
  File "/usr/lib/python2.4/site-packages/TurboGears-1.0b1-py2.4.egg/turbogears/database.py", line 246, in so_rwt
    retval = func(*args, **kw)
  File "<string>", line 5, in _expose
  File "/usr/lib/python2.4/site-packages/TurboGears-1.0b1-py2.4.egg/turbogears/controllers.py", line 343, in <lambda>
    mapping, fragment, args, kw)))
  File "/usr/lib/python2.4/site-packages/TurboGears-1.0b1-py2.4.egg/turbogears/controllers.py", line 367, in _execute_func
    output = errorhandling.try_call(func, *args, **kw)
  File "/usr/lib/python2.4/site-packages/TurboGears-1.0b1-py2.4.egg/turbogears/errorhandling.py", line 71, in try_call
    return func(self, *args, **kw)
  File "/home/hanyh/work/python/tutorial/tutorial/controllers.py", line 50, in add
    user = model.User.byEmail(email)
  File "<string>", line 1, in <lambda>
  File "/usr/lib/python2.4/site-packages/SQLObject-0.7.1-py2.4.egg/sqlobject/main.py", line 1271, in _SO_fetchAlternateID
    result, obj = cls._findAlternateID(name, dbName, value, connection)
  File "/usr/lib/python2.4/site-packages/SQLObject-0.7.1-py2.4.egg/sqlobject/main.py", line 1267, in _findAlternateID
    value), None
  File "/usr/lib/python2.4/site-packages/SQLObject-0.7.1-py2.4.egg/sqlobject/dbconnection.py", line 591, in _SO_selectOneAlt
    return self.queryOne("SELECT %s FROM %s WHERE %s = %s" %
  File "/usr/lib/python2.4/site-packages/SQLObject-0.7.1-py2.4.egg/sqlobject/dbconnection.py", line 761, in queryOne
    return self._dbConnection._queryOne(self._connection, s)
  File "/usr/lib/python2.4/site-packages/SQLObject-0.7.1-py2.4.egg/sqlobject/dbconnection.py", line 343, in _queryOne
    self._executeRetry(conn, c, s)
  File "/usr/lib/python2.4/site-packages/SQLObject-0.7.1-py2.4.egg/sqlobject/mysql/mysqlconnection.py", line 73, in _executeRetry
    myquery = unicode(query, self.encoding)
TypeError: decoding Unicode is not supported


我把FORM的字段ENCODE了也不行：如下
@expose()
    def add(self, email):
        # Remove extra spaces
        email = email.strip()
        # Remove null bytes (they can seriously screw up the database)
        email = email.replace('\x00', '')
        if email:
            try:
                user = model.User.byEmail(email)
            except model.SQLObjectNotFound:
        #        email = email.encode('utf-8')
                a = unicode( email, "utf-8" )
                user = model.User(email=a)
                turbogears.flash("User %s added!" % email)
            else:
                turbogears.flash("User %s already exists!" % email)
        else:
            turbogears.flash("E-mail must be non-empty!")
        raise cherrypy.HTTPRedirect('index')

怎么一回事情？