If you are using something other than LR to backup the LR catalog, you will need to make sure that LR is not running while you do the backup.
Thank You ManiacJoe, but still the same problem and I do the LR backup on exit from LR and LR is in Library mode. Funny is that after installation it did fine backups a few days, but then stopped to do, just telling that LR catalog is not answering and then closes LR. My LR is LightroomCC/6 via Adobe Creative Cloud. So I still need help.
I think the phrasing of "Lightroom backup catalog does not answer" was confusing me. I am going to assume you mean "Lightroom backup catalog does not respond" (program hangs).
While the backup dialog is shown, does the progress bar move if you wait long enough?
Is the hard drive light on indicating lots of activity?
Yes, now you undestand me. As I could not find any resonable solution I created a new backup catalog and this works fine. There must be something wrong in the old one, corrupted for some reason. The progress bar moved and then stopped when it was optimizing the catalog and told me: Lightroom backup catalog does not answer and closed Lightroom, when this happened it shows for a few seconds data of an picture, so the fault was in this picture data, I belive so.
Thank you very much for trying to help me !