Build app with Xcode 4 - it always show some error about PNG image

Solution 1:

You have to save your PNG files as NOT INTERLACED. Try to open the file in photoshop (or similar), save as, and select "Not interlaced".

Solution 2:

That happens when you have multiple entries for the image file in your project file. I have no idea why but I just removed all entries, reloaded the project and added the file again.