Error parsing XML: unbound prefix on library

Question

I am using three libraries in my project:

a. ViewPager
b. SherlockActionBar
c. PagerSlidingTabStrip

In my layout xml, I am getting the followin

Answer 1

there is already a root element

xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center"
tools:context="com.example.arifa.model.MainActivity"
android:weightSum="1">