Está anidando <activity>
etiquetas en su Manifiesto. Desarmarlos:
<activity
android:name="com.example.assignment.androidassignment.MainActivity"
android:label="@string/app_name"
android:theme="@android:style/Theme.Holo.Dialog" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.assignment.androidassignment.ViewAllEmployee"/>