Occasional 404 errors, fixed by re-saving permalinks

Hi there,

I have a particular situation. And I realy don't know where to look for an answer, so I was hoping you guys could help me out here.

This is what's happening:

-The normal pages on the website (not the buddypress or forumpages) give 404 “not found page” not always, but about twice/ three times a day.

-The solution is always resaving permalinks. After this everything works fine again.

- I’ve checked .htaccess during the error and when it works normaly. There is no difference between them... So the solution to change permissions of the file to 444 doesn’t work.

- The scary part is that we don't know what triggers it. We even checked the errorlog of the server. But with no result yet.

Do you know of something in the Classifieds or Custom Post Type plugin that can cause a conflict resulting in this?

If not, can you please help me how to implement flush_rewrite_rules($hard=false) into a (WP) cronjob that runs every hour? This would give me some room to think of another solution. This would be realy helpfull!

Note: I haven't updated both classifieds as the custom post type plugin to the latest version since I needed to hardcode some specif things for this client (I followed WPMU's instructions for these, see previous posts)

As always, your help is apreciated.

Kindest regards,
Steven