[Zope] startup error

Hi, Is this a known issue when starting zope 2.7.0-b1 on both windows and linux? Traceback (most recent call last): File "/opt/zope/lib/python/Zope/App/startup.py", line 48, in startup m=imp.find_module('custom_zodb',[INSTANCE_HOME]) ImportError: No module named custom_zodb Thanks, Mike