Same issue here, just posted a query and noticed this one. Looks to be a server problem.

Working fine earlier this week, I'm now getting this message and unable to progress game. Managed to get here on my Matrix password. So whats the problem?

I've been a regular multiplayer for several years but on attempting my first connection to muliplayer for just over a week, I received the following error message:-
"Server unable to validate your details - please contact support forums"

What do you advise should be my next step?

Dave F