MacBook air and internet connectivity

To address a 'dead' reception spot in our house, we've added a netgear plug extender, plugged in about half way from the Virgin hub on the ground floor and the 'dead' area two storeys above. This has solved the problem for the PC desktop and a printer on the top floor. Our iPhones and iPad have had no connectivity problems since adding the extender, but our MacBook air now cannot connect to the internet. A dialog box asks for a WP2 password to do so and when our existing password (WPA/WPA2 Personal) is entered we get the msg. 'invalid password'.

The only way so far to get connected successfully seems to be to bring the MacBook air next to another apple device that is on and connected to the internet. We have to do this each time we wish to start a new internet session.

What is likely to be the problem? It doesn't seem to be the Virgin hub, or the extender, as our other devices are not experiencing any connectivity problems. Are there an obvious answer? The MacBook air was bought in 2014 and is running mac os high sierra v.10.13.6,

Help appreciated.