Even you had valid icon in PNG.format along with its size (57x57), when you upload the binary to iTunes Connect, you may receive the following error message.
iPhone/iPod Touch: XXX.png: icon dimensions (0 x 0) don't meet the size requirements. The icon file must be 57x57 pixels, in .png format.
The solution is as below for Xcode 4.2.
Edit Project -> Build setting -> Packaging -> set 'NO' to Compress PNG Files