Why do some of my skins show up completely invisable?

Why do some of my skins show up completely invisable?

For some reason, when I apply certain skins on to the units, the unit goes completely invisable, except for the team colour. Whats the problem? I am using PSP v.9 if it helps anyone to figure out what the issue is.

its the alpha channel that's gone corrupt

Read my corrupted alpha channel tutorial.

Ah, thank you both. That helps alot.