That's because you haven't got the right API KEY for the Google maps widget.
When you sign the application, you have to use the same keystore and obtain an API key. You get the MD5 fingerprint of the keystore you are using to sign the application go here, http://code.google.com/android/maps-api-signup.html put the finger print and get the API key, then in your maps widget,
<?xml version="1.0" encoding="utf-8"?>
<com.google.android.maps.MapView
android:id="@+id/mapView" android:layout_width="fill_parent"
android:layout_height="fill_parent" android:apiKey="0G0LHKCCJvhmNvdpZijAqg76V63Cs6DTBbq2-Pw"
android:enabled="true" android:clickable="true" />
put the api_key
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