Noticed this for the 2nd time Yesterday this time whilst doing Ghillieglade, the game just dropped me back to the Desktop (I loaded up the Original Version of TERA that i also have installed (no steam login required)(also in seperate install location) and Game worked perfectly, i then told Steam to Check intregrity of the game files, this was done quite quickly and according to Steam 8 files were corrupt or missing and it redownloaded them for me, i then reloaded the Steam version as was in same place and all worked fine again.
The ONLY thing i can possibly come up with for this to happen was Norton was a bit over excited with a couple of files and removed them (yes i have told Norton to Ignore this directory) or maybe it might be windows defender, still not tracked down the EXACT cause (but letting people know if they have had this happen to them (it's not a major problem to sort out).
Also after an Update , Good idea to get Steam to backup TERA to a safe place (this can also be helpful for players with certain internet access) Example download TERA at work/college (Good Connection) Backup to a Mobile HD/USB device, then when at home (possibly You might have a limit to the amount of data you can download) and get this Version of Steam to restore backup at home (this has to have Internet Connection but its better to just have Steam download maybe a few Meg rather than a Massive 40 gig) u dont have to make a backup to move to another PC (with Steam same account details) you can just Copy the TERA directory found in Steamlibrary/Steamapps/Common.
Hope some of this EXTRA info helpful to others.
