"Skin images must be 64x64 or 64x32 pixel PNG files"

I finish making a new skin for a friend, and when i was going to put it on the launcher.
The launcher was saying it wasn´t a 64x64 pixels PNG.

I checked 3 times, and yeah. it was a 64x64 pixels PNG.

I close the launcher 3 times, and still saying the same error.

Idk how a bug like that can happend.