I only see team-colored shoulders of my custom skins?

Hiya! Some of my custom skins won't work. I've made them with photoshop, added alpha channel, selected them what I think is appropriately, saved them as targa, converted them to blp via Wc3Viewer (in which they work applied to a model), but when I try to use them in-game all I see is the shoulders, in team color.

Is this a common error? Does anyone know what I do wrong? Thanks for any answers :)

Alpha Corruption.. You need to re-modify the skin I'm afraid...

you just need to add a correct alpha channel...

How do I know if an alpha channel is correct?
I've painted on team-colored places, and selected everything except for the stuff that should be invisible. Is there anything more to do?

Also, some skins show invisible parts as solid, even though I've deselected them before saving.

EDIT: Thanks for helping me, btw :)