[Zope] IOError when packing database

[hostmaster]

Hi,

I am getting this error every time I try to pack my database from the
web interface:

------------
Site Error
An error was encountered while publishing this resource. 

IOError

Sorry, a site error occurred.

Traceback (innermost last):

      * Module ZPublisher.Publish, line 150, in publish_module
      * Module ZPublisher.Publish, line 114, in publish
      * Module Zope, line 171, in zpublisher_exception_hook
      * Module ZPublisher.Publish, line 98, in publish
      * Module ZPublisher.mapply, line 88, in mapply
      * Module ZPublisher.Publish, line 39, in call_object
      * Module App.ApplicationManager, line 353, in manage_pack
      * Module ZODB.DB, line 499, in pack
      * Module ZODB.FileStorage, line 1440, in pack
IOError: [Errno 13] Permission denied:
------------

My 'Data.fs' files are all owned by 'apache' user and I start my Zope
server with a '-u apache' command line.

Could someone please tell me what is going on.

Thanks.