BFBC2 "Unable to login" when entering serial number

Question

So I installed this "Origin" crap, bought, downloaded and installed Battlefield: Bad Company 2.

Now, when I launch the game and login with the same account I use to buy it in Origin, I'm asked to enter my serial number, which I do, but after hitting the submit button I get the "Unable to login" error, every, single, time.

I can't seem to find out where to enter it on the Origin or EA site, so how am I supposed to register my game?

Edit: Okay, so I found the "Redeem product code" in the Origin app, but now when I try to login to BFBC2 with the same account it still asks for the serial, but then says it's already in use, what the hell is going on here?

Answer

Searching this error message on the EA support center gets me this article. In a nutshell:

1. Turn off 'remember password' and log in again.
2. Delete the BFBC2 folder that should be located in your Documents folder and log in again.
3. Open a ticket if all else fails.

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