You should do the transaction in a Handler
as follows:
@Override
protected void onPostExecute(String result) {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute");
new Handler().post(new Runnable() {
public void run() {
fm = getSupportFragmentManager();
ft = fm.beginTransaction();
ft.remove(dummyFragment);
ft.commit();
}
});
}