Close on startup. Encoutered an unexpected error.

Everything's gone smoothly. Nothing out of the ordinary, up to today. When I do the exact same log-in procedure as always; punch in my pw and the one-time pw and press the Log In button, the game closes and I get the generic Windows error message that the program has encountered an unexpected error and needs to close.

What's going on? What can have caused this? I've done nothing to alter any files or anything that can have any impact whatsoever. And the internet have failed to assist me.
What may the problem be?

Shameless selfbump.