The link to the thread explaining what happened:
http://forum.bitcoin.org/?topic=1976.0

Basically the reason is a DDOS attack

You can access the site on https://mining2.bitcoin.cz/accounts/profile/

But you need to get your IP whitelisted to be able to start mining at the moment.

I need to PM someone in order to have my IP whitelisted and use the miner pool I was using until now which was victim of a DDOS attack.

Thanks a lot.