There's been countless threads on this very subject since at least December last year - the cause is basically too many people trying to access the free server at once, causing 'roadblocks' in a sense.
Basically, all you can really do is keep trying and eventually you may be able to access the DLS, or, the better option is to purchase a First Class Ticket from Auran which is basically a paid subscription to access the DLS (you get virtually guaranteed access to the DLS, at super-fast speeds too, unlike the free server which has a very low speed cap on it, when you can even access it).
Not everyone has the money to shell out on a First Class Ticket, but after buying one and seeing the difference, it's money well spent in my opinion.