[X2Go-User] Getting "Access denied for 'password'. Authentication that can continue: publickey, password", used to work

I've been running x2go from an xubuntu laptop client to an xubuntu desktop machine successfully for a year or so. It has now stopped working with a pop-up window that says:-

Access denied for 'password'. Authentication that can continue:
publickey,password
Access denied for 'password'. Authentication that can continue:
publickey,password

(yes, it is repeated like that)

I have moved from xubuntu 18.04 to 19.04 (via 18.10), would this have caused the problem maybe?

Whatever, how do I fix this? The error doesn't make much sense anyway as it's saying I'm not allowed to use password authentication and then it's saying I must use either publickey or password. FWIW I do use password authentication on my systems, for various reasons public key doesn't fulfil my requirements.

-- Chris Green