Just an FYI for folks who might come across the same issue I just did with PNG files.
My iPad project has PNG files in its resources. On the iPad simulator, these files load just fine with the juce loader. However on a real iPad the file load bombs out. It turns out that by default the XCode project “Compresses” PNG files put int the app resources - this turns them into ‘CgBI’ files (described here: http://iphonedevwiki.net/index.php/CgBI_file_format ) which juce cannot load. Turning off the compress PNG setting in XCode fixes the issue.