While trying to register TW2 i get an "invalid username" error. I'm pretty sure the username is correct as I have all the emails regarding TW1 registration right here. I've even registered TW1 again a few weeks ago (new machine) with this user.
Any help would be appreciated.

CDP is saying on thewitcher.com to register it with a NEW account and they are promising to look into merging existing accounts at a later date.

Same problem here.
I have a witcher account since 2007.
It always worked fine; no issues, no problem.
Exept now.
Everytime I try to register the game and put my id and psw it says "invalid username".

ps: I installed the game on my Xp desktop pc. And on that system the problem showed up.
I'm now trying to install it on my notebook (win7) hoping this would solve the problem.
I'll let you know.

Same problem. I've tried several times to register but even creating a new account fails.

Well i did create a new account with my existing user details. So this seems the way to go.

You mean you put the same id and psw in the new account? and it worked? O.O

Every time i enter my details appears a message saying that they already have it registered but it's impossible because i've tried with 5 different mails and usernames. I can't register muy copy and it's desperating.

Read this http://www.en.thewitcher.com/community/entry/6/

I have a slighty different problem. I clicked on "Register Game", then "Create an Account" but I cant input anything. The inputfields are there but they are not picking up my keyboard input no matter what i typed. Similarly for "Log in". Dont suppose anyone have the same problem?

EDIT: NVM, fixed it.

I have the same problem with you. :(

FIX - I GOT THE SOLUTION

First, you need to change font size setting of your window
by open your control panel - display.

Set font to Smaller - 100% (Default)
and log off & log in window again.

Hope this would help :)

So.
Having experienced the "invalid username" error on my Xp desktop I tried to install TW2 on my win7 notebook.
On this notebook when I type my id and psw in order to register the game it says "Connection Error. Try again later".
So I went back to my XP desktop and this time, instead of the "invalid username" error I got the "Connection Error. Try again later" error.
Same error on both computers so my guess is that they're trying to fix the problem.
And in order to do so they needed to temporary disable the connection.

Should we register on the Witcher.com first? And if yes, where on the site?

No luck logging in with my old thewitcher.com account... made a new one with the same username/email/password, lol... and now I get "error connecting blah blah..."

One would expect them to fix the registration servers in 6 hours since launch...

Ok, guys, after 8 hours... registered!
BUT it only worked creating a new id & psw (as for now you can create it not from TW site but from the game launcher).
If you're experiencing the same problem I had, this link might be useful [url=]http://www.en.thewitcher.com/community/entry/6/[/url]

ps: note that you may need to try several times typing your cd key.
I needed to type it 4-5 times before the system finally accepted it.
Also: keep the cd key format exactly as it is in your mail. Capital letters, slashes and so on.
I'm hoping you good luck.
And a lot of well deserved enjoyment <3

bruno