Mouth Shapes Dissapear After Moving Into .PGO Folder

Not sure what I’m doing wrong here but maybe you can help.

I created a .pgo file using Papaguyo and imported it into Synfig. I have 3 basic mouth shapes I drew on paper, turned into transparent PNGs in GIMP, and then imported them into Synfig. I adjusted their size and position relative to my character. However, when I drag them into the mouthshape folders from the .pgo file (AI, L, MBP, etc etc) the picture disappears. When I attempt to play back my animation, the mouths do not appear as they are suppose to.

What am I missing here?

Check out the tutorial. Hope it may help.