[Zope] Newbie question: Unhandled requests.

We currently started to run our site using Zope behind Apache using ProxyPass, when testing from the outside it seems that there many (about one-third) of the requests that are not handled by Zope, the browser seems to recieve nothing, (means the browser times out), this behaviour does not depend on the complexity of the document templates, it is an overall phenomenon (including management screens etc...). When pressing reload the things get okay most of the times, but it is annoying.. Any help would be appreciated..... thanks in advance. H.Grund. please replay to grundhan@cs.tu-berlin.de