Norwegian B738 over Slovakia and Poland on Jul 9th 2015, loss of communication

A Norwegian Air Shuttle Boeing 737-800, registration LN-NGG performing flight DY-3351 from Chania to Copenhagen , was enroute near Bratislava in contact with Bratislava, when Bratislava Center wanted to hand the aircraft off to Warsaw Center, however did not receive a reply. The aircraft continued, while ATC tried to raise the crew on emergency frequency 121.5MHz and contacted the airline who sent an ACARS message to the crew.