ClassCastException Android.view.viewgroup.$layoutParam

Question

 TextView txt=new TextView(productlist.this);
            txt.setText(author.get(groupPosition));
            TextView txt1=new TextView(productlist.this);
            txt1.setText(price.get(groupPosition));
            txt.setLayoutParams(new LayoutParams(70, LayoutParams.WRAP_CONTENT));  
            txt1.setLayoutParams(new LayoutParams(70,LayoutParams.WRAP_CONTENT));
            LinearLayout ll=new LinearLayout(productlist.this);
            ll.setOrientation(LinearLayout.HORIZONTAL);
            ll.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));  
           // ll.setGravity(Gravity.CENTER);  
            ll.addView(txt);  
            ll.addView(txt1);  

            return ll;

Hallo, dies ist der Codeschnipsel für eine Gruppenansicht in erweiterbar ListView was zu einem Fehler führt:

java.lang.ClassCastException Android.view.viewgroup.$layoutParam