color replacement tool stopped working all of a sudden

I was following a tutorial online and using the color replacement tool on a photograph.  Everything was working fine, I would select the color and then use the dropper + tool and it would change those colors to the selected color.  Then all of a sudden while in the same session still working with the same picture, all I could do was select colors and change nothing.  No matter what I try I can not get it to work again.  I have reloaded the same unedited picture into photoshop again and nothing but selection works.  I can not change any color in the photograph. It basically doesn't work at all.  What is going on with this program??  There are not too many options I can try within photoshop elements 14.  I have found zero relevant help on this subject.