When I connect to Titan via the Gremlin console it says... titangraph[cassandra:127.0.0.1]
Rexster however says... titangraph[cassandra:null] even though I can browse the same set of vertices.
Why is this? Rexster makes it look as though it hasn't managed to connect.
This message indicates that Cassandra did not start correctly.
Try starting Titan with the following:
titan.sh -c cassandra-es start
Have a look at /conf for additional configuration files.
Unless you really have to, I strongly suggest installing Titan 0.5.0 which comes with many useful features.
If you're starting with graph databases and Titan, I suggest trying with a single machine cluster or Berkeley DB as a storage backend. You may not need Cassandra yet.
You can also have a look at Titan/Aurelius official mailing list, I know the issue you're experiencing has been discussed there before: https://groups.google.com/forum/#!forum/aureliusgraphs. You can search for resources there (see, for example, https://groups.google.com/d/msg/aureliusgraphs/bviB6E5TZ-A/TJxQv0U7WQEJ).
In the meanwhile, you can try Titan v0.5.0 in Node.js by connecting via HTTP with https://github.com/gulthor/grex (HTTP client). The recommended way of connecting to Rexster is via HTTP (TinkerPop 2.x) or WebSocket (in upcoming TinkerPop 3, which Titan will support in a future version).