So lately I've been -very- frustrated with the beta opt-in as my battle.net application kept giving me the error, that there was a problem sending my information.
I found a workaround that, in my case, managed to make me able to submit my information.
PLEASE, BEFORE CONTINUEING MAKE SURE YOU'VE TRIED THE FOLLOWING:
Otherwise this is how I did (Please do know that application is not provided by Blizzard, but by a 3rd party. You are in no way forced to use it and you yourself are completly responsible for doing so):
I installed the application Spotflux from http://www.spotflux.com/. Once installed, I enabled it. What Spotflux do is connect to a VPN in America. Fancy word, eh? Well, to do this, Spotflux makes all your internet information go out a single port and come in through a single port aswell. As this is where it might help you ^^
SO HERE'S WHAT YOU DO!
1. Download Spotflux
2. Enable it
3. Go to http://battle.net/
4. Login (Please know that if you do not have an authenticator your account might be locked for suspicious activity)
5. Go to the beta profile settings page, and download the beta opt-in program
6. Once downloaded, run it
7. Click "Send"
Hopefully this will work for you! :) It did for me ^^ See you in game!