It would appear that Zenoss is trying to use SNMP to query a device, but the query is timing out. So I guess some simple things to check are:
Is SNMP correctly configured and running on the device in question?
Is the community string for that device correctly set in Zenoss?
I don't know if the documentation has been changed recently, but not too long ago it was not made clear that when you add multiple devices even though you specified the correct SNMP community string in the wizard, Zenoss would only use that to add the device and then ignore it.
You can find the current SNMP community string by going to a device (under Infrastructure) then selecting Configuration Properties on the left hand menu and then on the right look for the field called zSnmpCommunity