I had the same problem a while back. I think I ended up using BreezeBrowser to convert the files into 8bit. images. You may want to try and see if you can open them up with any other software and then convert them.
You may have some luck with this software and it is free! It has a convert feature and compatability with a lot of file types. Here is a link: http://www.irfanview.com/
|Orange-tip Butterfly by anisah|
from Nature's Colour Palette
|Windswept juniper by Kreber|
from Wind power