After reading this thread, I installed mp3gain and easymp3gain,it also brought in aacgain and vorbisgain with no errors.
I used easymp3gain to normalize my collection of mp3s. There must be a bug in the app though, because I kept getting a popup that said "Access Error..... continue risking file corruption". I could chose OK or Cancel. Cancel kills the app, OK lets it continue. It happened every time I moved the cursor. I had to leave the mouse alone during the entire process. It did finally complete the process and I think it worked.