whenever i trying to check iphone 4 in debug mode it will throw following warnings and it will not run in debug mode.
warning: UUID mismatch detected with the loaded library - on disk is:
/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.0.sdk/System/Library/PrivateFrameworks/MobileIcons.framework/MobileIcons
Seems like the Library on your disk (that means your XCode version) and your iPhone have different iOS versions running. Normally you can ignore such a warning, but if you say it isn't starting, try to update Xcode & your iPhone. Then delete "/Developer/Platforms/iPhoneOS.platform/DeviceSupport/" and after this clean and rebuild your project.
This worked for me, with a similar error.