The official site has posted this press release from the Sonisphere organizers:
Due to logistical problems the local promoter, Marcel Avram and Balkan Entertainment have unfortunately decided to cancel this year's Sonisphere Festival in Sofia, Bulgaria. Everyone at Sonisphere have worked diligently to try and get the problems rectified but unfortunately these problems cannot be resolved. Sonisphere apologises for the cancellation and any inconvenience this has caused. Unfortunately these circumstances were out of our control.
Tickets will be refunded in full starting June 15 and until July 15. Tickets bought online at www.eventim.bg can be refunded at Eventim's head office in Sofia, at 43 Dospat Str. Inquiries about refunds can also be directed to firstname.lastname@example.org.