Consider using FM Server software. Solves your problem and gives you the ability to schedule automated backups of your files.
Thanks for the suggestion jens, but I don't like it when suddenly messages apear while I don't know how or why they are generated. I am sure I did something to trigger the share-message but I also want to know how to correct this because the programm "Main" was working fine for a long time before.
So when someone has a good idea to handle the problem, I will be gratefull.
Thank you for your post.
Launch FileMaker Pro, and select "Open Remote..." from the File menu. This is the proper way to select a FileMaker Pro file when it does not reside on the local computer. You should not open it directly from the server.
The only way to avoid this message is storing the databases directly on the machine which opens them as first FM client (when working without FM Server).