The terms of service forbids the modification of the ini files (amongst other things) and can result in the suspension of one's game account. However, a community manager has stated that "for the sake of clarification, you won't get banned for changing a line in a .ini file".
It is possible to edit a .ini file to alter the in-game FOV.
...\Program Files (x86)\TERA\Client\S1Game\Config
Underneath this line, add a new line with the following:
Where 'N' is the desired FOV value - note that 100 is a reasonable value to set this to. Also note that there should be no semi-colon at the beginning of this line unlike the lines which follow it. A visual representation of the change in FOV value can be seen here.
press "x" to activate ingame
This issue is usually solved by doing the following:
If it doesn't work, disable your Anti-Virus. Panda Cloud Anti-Virus, for example, causes this problem.
Or try downloading the patch manually here and then extracting the game.version into your Tera folder. You will need to extract the top level archive first and then extract the game.version from the second archive.
There are several reasons this issue may occur, and it is usually characterised by the login page on the launcher constantly refreshing.