After the last upgrade from 5.1-OD-13 to 5.2-OD-3 on July 8, 2013, some OnDemand Confluence instances cannot create new Spaces.
Clicking the 'Create Space' button should bring you to the newly created Space homepage, however the Space and page are never created, resulting in a 'page not found' error.
The following message appears in the log:
However no other error appears (even with debug logging enabled).
Turn off the default space logo in Confluence Admin -> Default Space Logo (the URL should be https://example.atlassian.net/wiki/admin/configuredefaultspacelogo.action). This will allow spaces to be created.