You was right. The quality of the bulk DVD (falcon) is week. The program default burning speed is x6 . I burned with 4. It shows a disk error. Finally the x2 speed produced the right quality. Thanks.
I have combined this post with your original question to maintain the thread of the post here
Please keep any replies on a particular question/topicin the same thread - you can answer your own question to post further information - this will allow others to follow the question/answers/solutions.