You are right. The problem was with the DVDs. I have tried with three new (write-only) and all were saved properly. It was strange but the first trials with rewritable DVD were corrupted. In any case, thank you for your replies. Problem solved.

Thank you fo the prompt reply. Indeed if manual chapters are not defined the box can be cleared. However, I have tried burning three DVD and these chapters are not created and titles can not be set.
Am I doing something wrong?

After installation it is not possible to de-activate
"Automatic chapters every 10 min"
in DVD authoring for DVR Studio 1.66 Prof.
This box is ticked and it is not possible to uncheck it.
Can you help? I will appreciate if you can help.