The problem has been solved...
In the network configuration of server I removed the fixed IP and instead I used DHCP.
So the IP server has changed from ...1.69 to ...1.186 and now Calibre content server works great !!!
On the router probably there is some rule, unknown for me, linked to the management of the low addresses of the LAN. In fact, now the SMB protocol also works, while before it did not allow me to share folders (client network time out).
I thank everyone for the advices (Kovid Goyal included) and for the time dedicated.