The legitimate Temple Run 1.0.2 for iOS 4.2.1 has an MD5 checksum beginning with f8c3a2b... . Always check the file in a hex editor for the string "MinimumOSVersion: 3.0".
Have a copy of the original IPA? Upload it to the Internet Archive. Preserve the bit.
: Older versions of iTunes still allowed for manual IPA management. You can drag and drop the IPA into the "Apps" window and sync it to your device. AppSync (Jailbreak Recommended)