It's hard to find information about this festival. It has changed its name from Rock the City to Rock over Bucharest. At the moment the old pages remain and the new ones haven't been created. So, I'll post those and update later.
Tuborg GreenFest is an annual series of rock music events that takes place across Eastern Europe during the summer months. Since 2005, Danish beer makers Tuborg, part of the Carlsberg Group, have brought together well-known rock bands and artists for one-day festivals in Russia, Serbia and Ukraine. 2008 saw concerts held in Bulgaria and Croatia for the first time, and in 2009 GreenFest premiered in Romania.
Facebook: http://www.facebook.com/TuborgGreenfest2012
Ticket sales begin on 2012-11-01