Mailman giving error : Uncaught runner exception: [Errno 13] Permission denied

Issue

Here is the error log:

Nov 15 08:54:06 2011 (1506) Archive file access failure:
        /var/lib/mailman/archives/private/unrealengine-news.mbox/unrealengine-news.mbox [Errno 13] Permission denied: '/var/lib/mailman/archives/private/unrealengine-news.mbox/unrealengine-news.mbox'
Nov 15 08:54:06 2011 (1506) Uncaught runner exception: [Errno 13] Permission denied: '/var/lib/mailman/archives/private/unrealengine-news.mbox/unrealengine-news.mbox'
Nov 15 08:54:06 2011 (1506) Traceback (most recent call last):
  File "/usr/lib/mailman/Mailman/Queue/Runner.py", line 120, in _oneloop
    self._onefile(msg, msgdata)
  File "/usr/lib/mailman/Mailman/Queue/Runner.py", line 191, in _onefile
    keepqueued = self._dispose(mlist, msg, msgdata)
  File "/usr/lib/mailman/Mailman/Queue/ArchRunner.py", line 73, in _dispose
    mlist.ArchiveMail(msg)
  File "/usr/lib/mailman/Mailman/Archiver/Archiver.py", line 200, in ArchiveMail
    self.__archive_to_mbox(msg)
  File "/usr/lib/mailman/Mailman/Archiver/Archiver.py", line 169, in __archive_to_mbox
    mbox = self.__archive_file(afn)
  File "/usr/lib/mailman/Mailman/Archiver/Archiver.py", line 157, in __archive_file
    return Mailbox.Mailbox(open(afn, 'a+'))
IOError: [Errno 13] Permission denied: '/var/lib/mailman/archives/private/unrealengine-news.mbox/unrealengine-news.mbox'

Nov 15 08:54:07 2011 (1506) SHUNTING: 1321365184.2336111+4fb0ddc63c27b1184d1f3392efd5d3a7762f1fad