fingpngWindows not fully converting

I found fixpngWindows to use for converting the png files in the filesystem for iphone but it only converts half the image then says it completes but its not really complete. can anyone figure out y it is doing this? or is there another program i can use with windows?

Devices:
Phone: iPhone 4 - iOS 5.1.1 Jailbroken
Laptop: HP Envy DV7 - Win 8