WiFi sign-on issue

I have a Time Capsule that is my Wi-Fi Router. The Network name is "Dave's Wi-Fi Network", I have been connecting to it for several years from my MacBook Pro, but recently something has changed. When I open the laptop or turn Wi-Fi OFF and then ON, the Wi-Fi icon in the Menu bar shows it is searching, but that it can't find anything.

If I go to the Menu bar and pull down the list, my network does appear and clicking on the network name causes an immediate connection, but it also give me the error message;

I have not clicked the Reset to Defaults button because I have no idea what things will be reset when I do. When I click Cancel, I get the following error message.

However, I am connected to network and everything works fine until I have to reconnect to the Wi-Fi network.

Anyone know what is going on and how I can fix it?

Thanks,

Dave