[Zope] Zope 2.7 - sporadic service hangup

Hi, we notice two or three times a day some kind of hangup of the zope service. After hangup there is no response requesting urls/manage interface cannot be accessed, too. Restarting the zope service resolves all problems until the next hangup. No errors in zope logs! Seems to work everything fine ... We use Zope 2.7.5-final, python 2.3.5 on Debian, to access LDAP LDAPUserFolder, ZOracleDA for Oracle Connection. I know about problems with ZOracleDA - but not resulting in hangups. What could be the reason? What can I do? Marcel