This looks similar to the issue I encountered with my new Zenoss install. My issue turned out to be from me changing the system time after installing Zenoss. Once I tried to log back into Zenoss did not like that the new system time was in the past and threw similar errors...I don't think mine said POSException but it definitely was similar.
Walking through the steps in Fixing ZODB Integrity from the Wiki resolved my issue http://wiki.zenoss.org/Fixing_ZODB_Integrity_Issues