I can't log-in through the green Steam button

[TheOptimiser]

Hi guys, when logging-in the game via the Steam button I get the message Registration Error, does anyone else have the same problem as me?
Logging-in normally by typing the username and password allows me to get into the game, but when I try to get into the game via the Steam button I encounter that problem...

I couldn't log-in in to the game and I thought, let's change the password and introduce a new one and maybe that fixes the problem, I've cleared the password field(below the green Steam log-in button) and then pressed again the green Sign-In Button, after that it appears a white box where I need to introduce my password for the current account, when introducing it it appears this error: RegisterAccountPopUp - IO Error and a 2 rows long error code...

I've reset my password for the second time, same problem...I can enter the forums, I can enter the game via the 2 white boxes on the left side which tell me to write my username and password, but I can't connect in the game via the green Steam button...

The exact same error appears with the exact same code...

Any help?

[TheOptimiser]

Here's a picture with the error I encounter when introducing the password via the green Steam button:

https://ibb.co/wBkwk71

[TheOptimiser]

I did the following steps and none of them worked:
-installing Adobe Air/reinstalling it
-installing and reinstalling the game
-closing and reopening Steam
-restarting the PC
-turning off the firewall and back on
-changing my password several times

None of these worked...I still have the same error and it's frustrating....
I can play the game on browser, I can connect in the game using those 2 white boxes designed for Username and Password, but whenever I press the green Steam button, it asks me the password(the username is already listed there), and after I introduce the password that error occurs...

Please help me, I have over 1200 hours in this game, one of my favourite ones, and I am unable to play properly on Steam.

Any help is very much appreciated.

Thanks!

[Jerme]

Moving this thread to Steam Bug reports.
I do not know what this could have caused, atm. May I know which OS you are using?