Hello, i have the same problem. All these years, all of my Vegas versions have been able to read mp3 files. But suddenly it did not work anymore. I reinstalled vegas now for the second time, but mp3 still doesnt work.
Hold down the CTRL + SHIFT keys at the same time AND ALSO AT THE SAME TIME double click program icon on Desktop to Boot program. Select Delete all Cached Application Data and then press Yes. This will restore program to Factory Default Settings.