Changing the color of an area

I collect and catalog pins.  After scanning, I use Photoshop Elements to clean up the pin scans, especially the backgrounds.  I had been using the lasso tool to define an area that I needed to change the color or make the color uniform.  Once the area was defined, I would then fill in the area with the desired color.  This procedure no longer works.  I get an error message: "No pixels are more than 50% selected.  The selection edges will not be visible."  Why did my procedure quit working after more than two years of using it?  Is there a setting somewhere that somehow got changed?  I use an Epson flatbed scanner and have not changed any of the settings when I scan the pins.