Does your password have weird characters?
Is it possible that your server hasn't the locales/keyboard configured to match yours?
A simple way to test this is is by using just a simple letters OR numbers only password and try to login.
No weird characters - it's only open to local network access, so it's a simple alpha-numeric password. Password being entered is 'correct'.
I'm wondering if it's something related to my ISP, as this may have occurred around the time I had to contact them to resolve an issue with access to my work VPN, which the newer generation of Sky routers appeared to not play nicely with.