SOLVED! "This Nickname is not registered on this server"

[Pine9]

Hi.
I'm coming back to the game after a while, my nickname is the same as the one in this forum which is 'Nor_Green'.
I can connect to the alternate server with no errors; but can not connect to the official one.
This is the full error "The nickname 'Not_Green' is not registered on this server, we will disallow unregistered nicknames"
Also I went away from the game for a while because I wasn't able to log in(I don't remember what was the error but I'm sure it had something to do with the server itself not the nickname)... but VPN fixed that.
Edit: Windows 7 64bit, Wesnoth version 1.16.2(Steam)
P.S: I'm not using VPN right now.

Edit again:
Sorry here's the full report:

Spoiler:

======================================================================================================================
The Battle for Wesnoth version 1.16.2 x86_64
Running on Microsoft Windows 7 Service Pack 1 (6.1.7601) x86_64
Distribution channel: Steam

Game paths
==========

Data dir: E:\Steam\steamapps\common\wesnoth
User config dir: C:\Users\USER\Documents\My Games\Wesnoth1.16
User data dir: C:\Users\USER\Documents\My Games\Wesnoth1.16
Saves dir: C:\Users\USER\Documents\My Games\Wesnoth1.16\saves
Add-ons dir: C:\Users\USER\Documents\My Games\Wesnoth1.16\data\add-ons
Cache dir: C:\Users\USER\Documents\My Games\Wesnoth1.16\cache

Libraries
=========

Boost: 1.74
Lua: 5.4.2
OpenSSL/libcrypto: 1.1.1i (runtime 1.1.1i)
Cairo: 1.17.4 (runtime 1.17.4)
Pango: 1.48.0 (runtime 1.48.0)
SDL: 2.0.12 (runtime 2.0.12)
SDL_image: 2.0.5 (runtime 2.0.5)
SDL_mixer: 2.0.4 (runtime 2.0.4)

Features
========

Lua console completion: yes
Win32 notifications back end: yes

Current video settings
======================

SDL video drivers: [windows] dummy
Window size: 1366x768
Screen refresh rate: 60
Screen dots per inch: 96.000000x96.000000
Screen dpi scale factor: 1.000000x1.000000

Current audio settings
======================

SDL audio drivers: [wasapi] directsound
Number of channels: 2
Output rate: 44100 Hz
Sample format: signed 16 bit little-endian
Sample size: 4096 bytes

Installed add-ons
=================

No add-ons installed.

[Pentarctagon]

The secondary server doesn't require a forum account to be registered, but the primary server does.

[Pine9]

The secondary server doesn't require a forum account to be registered, but the primary server does.

So why can't I log in even though I have a registered account? I tried to log in but nothing happens when I click on the 'OK' button. (double checked password and nickname, they are correct)
Also What is the reason behind having a server requiring a registration and haveing one that doesn't? Is the first server more secure or something?

[Pine9]

The secondary server doesn't require a forum account to be registered, but the primary server does.

Ok, I'm sorry I made a mistake; I was trying to log in with 'No_Green' which is missing a T!
It's 'Not_Green'
The issue is resolved! Thanks.