Hey, I need help converting PNG files off iPhone 4 running iOS 5.1. The PNG's I'm particularly interested in converting are in /system/library/coreservices/springboard.app

Whenever I try to convert them they either dont convert and give out an error message or they only convert half way. Ive tried using iFunBox, PNG Converter, iPhonePNG Converter and about 5 other iPhone converters that vary from java to python scripting that people have made themselves to fix issues other converters dont but none of them work, has anyone had any success converting PNG's off iOS 5?

Photoshop and preview will open them but there wont be any image in the file and im running intel MBP 10.6.8.