problems converting aup to mp3 with audacity-portable 1.3.14 Unicode

Hi all. My problem is I have multiple tracks of audio recordings of original Audacity portable. Some could export them as MP3 playback and other 8 continued (all tracks (28) belong to the same project) to be exported as MP3 playing but no sound, only noise, take up space (they are recorded, you see the graph) . That may be happening? the defective copy and save as new project, but is the same. The format is escuhan audacity perfectly, but other programs will. Thanks for what you can help me. salutations