Java returns "ScrollView can host only one direct child" when there's only one direct child

I have my own custom made ScrollView as a main View of my layout, which contains one single FrameLayout and every other View is put inside it. It looks like this (this is sm_layout.xml):

<com.effeleven.utils.CustomScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/scrollView"
    android:background="@color/white"
    android:clickable="true">

    <FrameLayout...>

</com.effeleven.utils.CustomScrollView>

I did not have this exception thrown when I used the default Android ScrollView. Now I need a custom one, because I need to handle the scroll events inside the ScrollView (I have a mapFragment and ListView, which I can't replace with anything, because I follow a design pattern). What can be causing the exception, since my CustomScrollView contains only one FrameLayout, just like the previous ScrollView did?

This is my CustomScrollView class:

public class CustomScrollView extends ScrollView {

public CustomScrollView(Context context) {
    super(context);
    LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    layoutInflater.inflate(R.layout.sm_layout, this, true);
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    final int action = ev.getAction();
    switch (action)
    {
        case MotionEvent.ACTION_DOWN:
            super.onTouchEvent(ev);
            break;

        case MotionEvent.ACTION_MOVE:
            return false;

        case MotionEvent.ACTION_CANCEL:
            super.onTouchEvent(ev);
            break;

        case MotionEvent.ACTION_UP:
            return false;

    }

    return false;
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    super.onTouchEvent(ev);
    return true;
}
}