Multiplayer Login Error

[Saureus]

Hello, I received the following message when trying to log in to a multiplayer game (see image). I used the same saved login parameters, and I confirmed my username and password, so I'm not sure why I'm getting this error. I tried several configurations with and without a VPN, but this had no effect. Does anyone know how to address this issue?

[Saureus]

Never mind, the issue vanished as mysteriously as it appeared...

[VANorm]

I've gotten the Error 6, and also sometimes get Invalid Serial Number. This is launching from Steam.

It's been a long time since I used Matrix's PBEM++ but this sure seems like some flaky programming.

[VANorm]

Here's the error when I try to Register:

Invalid Serial Number. Re-install game with correct serial number

I had launched the game from Steam.

I can successfully log-into my Matrix account, on their site.

Norm

[VANorm]

Looks like it works with my Slitherine password, not my Matrix - D'uh.