Aero - Cannot keep the transparency on a small image

Hi,

I cut my painting in layers and then save each layer individually so I can have them as an image with no background in aero. It worked for all the bigger images.  However, it looks like all the small ones (size of beads or eyes) or not keeping the transparency when I import them into Aero.

I tried the mask and the alpha channel.  My files are all saved as png.  No matter how I try, the small images don't keep the transparency in Aero.

Any suggestions?  Thanks a lot!!