Aion uses peer-to-peer torrent technology to deliver its updates. Make sure that this protocol is allowed through the firewall. Another problem is that you will need to wait a while since the process will take from a couple of minutes to hours. Another solution is to re-install the launcher but I believe is not the case since you can download updates.
Most likely you have tried to update during the maintenance hours because Wednesday is the day where all the servers are down and the maintenance is in progress.
