After watching the backup for a few days I found a few interesting things I did not know and want to share with others that may also not know (Those that know everything anyhow may want to stop reading here.) Note: I have a Windows 7, 64 bit System with MC 17.
1. The library that is used "live" is stored in the directory C:\Users\[User Name]\AppData\Roaming\J River\Media Center 17\Library\
2. The backups. (manually or automated) go to that directory that you configured in Tools-->Options-->File Location-->Program Files (the last line in the window).
I could easily do manual backups and they ended up where expected as a .zip file with the data added
I did not see automated backups since long.
I changed to run MC 17 as administrator and then it seems to work. There is a backup of the library in a subdirectory of the above specified one which is called "J River" and has no zip file, however all the files and the structure of the one used by the program (C:\Users\[User Name]\AppData\Roaming\J River\Media Center 17\Library\...)
It seems that the automated backup always replaces (writes over it) the old backup. So you do not have a history of backups, which could become an issue, if you recognize an error in your library relative late after a few days. If you did not do a manual backup, you have nothing good to go back to.
3. Additonal Backup. I am using SyncBack Pro for regular backups of all my data and mp3 files. So I decided to have more control over the Library backup and created a backup job with SyncBack Pro. And there may be other software that does the same job as good. The backup job creates a backup of the library in C:\Users\[User Name]\AppData\Roaming\J River\Media Center 17\Library\ to the Library Back directory every day at the same time (when the PC is running, when not it's skipped). The backup is automatically condensed into one zip file. To preserve more than one backup, I have decided to name the files with a date parameter. By that I am keeping a long list of backups and can frequently go back an delete the very old ones.
Below is how this looks on my PC.
I have tested the restore with these backups created from SynBack Pro. It works. And you still can decide to do a manual backup whenever you think of it.
I feel much better now knowing when and what is saved where.