As of May 7, 2015, any keys created will no longer have a limit on the number of channel groups that can be created. Key created prior to this date have a limit of 100 channel groups per namespace and you can create up to 100 namespaces within a single PubNub key set (publish/subscribe keys) for a total of 10,000 channel group (100 namespaces x 100 channel groups).
This means that namespaces are no longer supported and listing channel groups is also not supported. If you are already using these APIs, please be aware of this when using your codebase on a newly created key.
Contact support if you would like your old keys configured to have unlimited channel groups (or new keys configured to have limited channel groups).