Suddenly Cannot find block files and cannot export

I recorded a very important interview directly with Audacity. And I just have the .aup file. I saved it correctly. But today, when I opened audacity, it couldn’t find around 200 small .au blockfiles. But the folder is there… now there are a lot of silent parts in the interview… and Audacity doesn’t let me export the remaining material as an mp3. So I cannot fix it and I also cannot save an mp3 (or Any other file like wav) of the remaining material. I am using audacity 2.2.1. and work on a Mac 10.14.12. Please help me!