I'm using my old Sony Xperia Z1s on my home Wi-Fi. The phone can see the network, but won't connect to it. I've connected another phone to the same network, so I know I'm typing the password correctly. When I click on the network to connect to it, the signal bars go all the way down for a split second, then come back to full with the network still saying it's "Saved". Every now and then it'll say authentication problem, but I know the password was input correctly. The most frustrating part is this started happening today. It's been working perfectly for over a week.