my iPhone 6 will not recognise my personal wifi password

After backing up my iPhone 6iOS 9.1 it will no longer accept my password to connect to my personal wifi router. I get the message: "Incorrect password for ..."

I have reset network settings. I have not changed my wifi password.

My other devices (Apple iPad and an iPhone 3G) are all ok.

Can anyone help with this? I've looked online and it seems that it happens quite frequently.