There are a couple of things to try.
Firstly, did you remove/rename the beginning video files so they don't run whenever you start the game? If this is so, then you need to restore them. They removed that little workaround a while ago and your client will chuck a hissy fit and try to download everything again or not work. If you don't have them, let me know and I can provide them for you.
Secondly, check out this link and try these. I know you aren't getting the error but it's kind of the standard 'what to do when Tera won't work' thing.https://tera-support.enmasse.com/app/answers/detail/a_id/267/~/download-error---checksum-%2F-unknown-file#Direct
TigerShark wrote:Any way for the latest client to be available on games.on.net? The request form stated that the download link request must be a direct download, which I could not find. Got me puzzled over how the client is hosted here....
I was wondering this myself as I can't spare the quota to download the full Rift client after I accidentally logged in and started my free month count down but need to wait till the end of the month to download it now.