As @JoeyH hinted at, you will want to make sure the .pcl file exists. What you have shown in your screenshot is the .pcl.data folder, you will need both the file and the data folder to open a .pcl project (one of the advantages of the .pclx format is that everything is bundled together in a single file).
The good news is that you’ve definitely got the frames still, so worst case scenario (ie. you deleted the .pcl file), you can start a new Pencil2D project and import those frames, eliminating the need to redraw them. If you use the import image predefined set, and select all the images in that folder (just the images), you should be able to import them with the correct spacing and split onto separate layers. That feature can sometimes be hit-or-miss, so you can fall back to the image sequence import and import all the images for a single layer at a time and space them out manually (though it doesn’t look like that matters in this case).