Connection Error 300

[ColonelKAITO]

Hello

Every time I try to access the game, I am thrown out of the game by error code 300. This happens on the character selection screen, and only after I click "start game" with my character selected. Choosing different characters does nothing, as I am still thrown out of the game. 

I have tried consulting past forum posts about this, but none of them are answering my problem, or addressing the issue I am having. I cannot even find out what error code 300 means. I'd appreciate any advice on fixing this.

Just as a sidenote, I'm running the vanilla version of the game with no modifications or external software effecting the game other than the default stuff that comes with the initial install.