Make sure you have write permissions defined in the manifest file:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
The File.renameTo() method will fail under the following conditions:
- Write permission is required on the directories containing both the source and destination paths.
- Search permission is required for all parents of both paths.
- Both paths be on the same mount point. On Android, applications are most likely to hit this restriction when attempting to copy between internal storage and an SD card.
As described in the documentation: http://developer.android.com/reference/java/io/File.html#renameTo(java.io.File)
Additionally, I would verify that the newFile path is what you expect it to be.