Android: strange error in Manifest

I was modyfing my android app, and I was trying it on real device (Run Application in eclipse) and all was working good. So When I was satisfied of my changes, I opened the Manifest in order to modify the version for releasing it, but WITHOUT ANY CHANGES in Manifest an error occurred at line: ``` <uses-permission android:name="android.permission.INSTALL_PACKAGES" /> ``` the error is: ``` Permission is only granted to system apps ``` How is this possible? I builded my application many times using this line.