Re-install settings application. I have compiled Android Source codes and get settings.apk now I wonder can I install that application on my phone ? When I try to do that my phone say "CAnnot install application" what can I do to install that application ?
System application are odexed, which means the code part it extracted and kept separate and also some crucial parts of the application are kept in framework.jar. If you want to copy your freshly-compiled application to your phone, you have to deodex it first, which restores the missing parts and only then you may replace /system/Settings.apk with your new file. And, please, make sure you delete old /system/Settings.odex file, otherwise it won't work.

As usually, it's recommended to save old Settings.apk/odex files just in case when something goes wrong.