Some audio tracks do not play back

Hi,

I am using my Premiere Pro CC Project on another computer now, and some audios do not play.

Every sources were found and the timeline shows all clips correctly, but (random) audio clips sometimes the voices sometimes the background music just do not play back.

e.g. the video is playing, the background audio changes but the next one does not play back, only one of two audio tracks At another point just all audio tracks do not play back (it is quite random)

Thanks for help!!!