Why won't my Minecraft skin change for my server?

I have bought Minecraft. It isn't the cracked version. I have downloaded the skin and clicked to change it, but I can't see it and neither can anyone else. The strange thing is, it is only on the server I created. Is there a reason for this? If so, how can I fix it?

If you haven't migrated to a Mojang account yet, please do so and this may fix the problem (first link)

This reminds me of what happened in 1.8.4 so if you are running a version less than that, you can change this from that first launcher screen. If you're on a crappy server that is running an old version this, of course, could be a problem and you might want to beg the owner or one of the ops to upgrade the thing… (see second wiki link section: changes)

(Editedit: OH YEAH reading the link I sent you. Reminds me that you may have to re-upload the skin as a.png (most image editing programs will do this for you if you just 'Save As' and re-name the file.)

(Edit: oops had links in wrong order derp.

https://account.mojang.com/...om/migrate

http://minecraft.gamepedia.com/....com/1.8.4

Its that microsft bought minecraft and then they changed so you can't have skins on some servers because some one have a dickskin.
so they invented som stupid thing that it is a 50% chance that you get steve skin or a gril skin.