Both languages, at the core, are not that hard to learn, and also to learn the concurrency features they provide. In fact, Scala actors are influenced by Erlang actors. I would go to both of them, take your time looking at their construct, do some tests in concurrency problems, etc.
If you know Java, Scala will be more natural, as Erlang is more like prolog. If, on the contrary, you're more oriented towards mathematical or logical type of languages, start with Erlang.
