The current version on PTS (2.6.1) crashes every time shortly after launch (e.g. in the gamma settings screen or shortly after that).
Current production version of TESO (2.5.x) works fine, so did all previous versions.
Tried 32/64 bit clients.
Tried full (!) reinstall.
Account has admin privileges.
Win7 / MSI GT70 (nVidia 780m), enough RAM (16 Gig), enough hard disk space.