Sometimes logging in with default admin account leads to a blank page with the URL /portal/xlogin (e.g. https://sakai.cet.uct.ac.za/portal/xlogin). Manually entering the URL /portal/ leads to a correctly logged in session.
This seems to be associated with this warning in catalina.out though the problem is not easily reproducible:
WARN: addSession: already have a session (2005-11-01 10:35:23,521 TP-Processor7_org.sakaiproject.component.adaptor.UsageSessionServiceAdaptor)
The problem may also be associated with logging in to another instance of Sakai (2.0.1) on the same server on a different port or some combination of events.