Normalizer won't produce results.

I was recently on a song project, and needed to 'Normalize' the track. However (and this is the FIRST time I had experienced this) the normalizing action would not function for me. I had undergone the procedure many, many times before - without issue. But, now, I cannot get it to normalize my tracks.

Any ideas on what I might be able to do, in order to correct this?

Normalizer won't produce results.