trac-admin get error message so can't go on

[rue@…]

Once I execute the trac-admin command , the error messages shown as below.have you seen that?

Upgrading Database
Creating work_log table
Traceback (most recent call last):
  File "/usr/bin/trac-admin", line 8, in <module>
    load_entry_point('Trac==0.11.6', 'console_scripts', 'trac-admin')()
  File "/usr/lib/python2.6/site-packages/Trac-0.11.6-py2.6.egg/trac/admin/console.py", line 1321, in run
    return admin.onecmd(command)
  File "/usr/lib/python2.6/site-packages/Trac-0.11.6-py2.6.egg/trac/admin/console.py", line 138, in onecmd
    rv = cmd.Cmd.onecmd(self, line) or 0
  File "/usr/lib/python2.6/cmd.py", line 219, in onecmd
    return func(arg)
  File "/usr/lib/python2.6/site-packages/Trac-0.11.6-py2.6.egg/trac/admin/console.py", line 1159, in do_upgrade
    self.__env.upgrade(backup=do_backup)
  File "/usr/lib/python2.6/site-packages/Trac-0.11.6-py2.6.egg/trac/env.py", line 464, in upgrade
    participant.upgrade_environment(db)
  File "build/bdist.linux-i686/egg/worklog/api.py", line 184, in upgrade_environment
  File "build/bdist.linux-i686/egg/worklog/api.py", line 129, in do_db_upgrade
pysqlite2.dbapi2.ProgrammingError: Cannot operate on a closed cursor.

[Ryan J Ollos]

I've seen users in other threads with similar issues say that moving the database connection code into the try block fixes similar issues, but I'm not sure why that would be the case:

try:
    db = self.env.get_db_cnx()
    cursor = db.cursor()
    cursor.execute('SELECT MAX(version) FROM wiki WHERE name=%s', (user_manual_wiki_title,))
    ...