Quote from DogsRNice
its not "steve.png" unless they changed it its char.png
Quote from EnderRulesMC
it is not "steve.png" it is "CHAR.PNG" (No caps)
Quote from _WhiteDragon
You could also just go and log into minecraft and use the 'upload skin' as well if it is easier. I'm not saying your way doesn't work but just suggesting an alternative if you're having problems.