[Zope] Zope Instability

Hi, We recently setup a Zope server and it has been running great until this morning when it stopped responding, twice. There are no errors, core files or indication of a problem except that the server stopped responding to http requests. All processes were still running and a simple restart remedied the problem both times. Has anybody had any similar problems, advice, etc. We are running two Zope servers serving two different sites. Both servers run as the same user. Thanks, --Rob Zope Newbie