Solved Beating difficulty and re-joining realm causes "Unrecoverable internal error"

Good evening!

After going through all the installations, compatibilities, -3dfx glides etc., I started playing yesterday. Almost everything works fine, till someone rushed my Sorceress on Normal HC and wanted to help me on Nightmare too.
Knowing from past that you can't host a game on higher difficulty, unless you exit Realm and enter with your Character again, I quit to the character selection screen and while trying to enter again... I received "Unrecoverable internal error [numbers and letters here]"

I tried to open the game again, as this person was waiting for me to host, but it didn't worked. I tried to launch from game.exe, EuropeBattle.exe, Loader.exe, but none of these worked. It was adding more and more game.exe that I couldn't terminate copies to the opened processes.
I terminated this GameGuard process and game.exe processes somehow terminated, but I was unable to launch the game again. It didn't wanted to start.

Some time later I restarted my PC and the game was working again.

Today, I finished Nightmare difficulty with my Sorceress. I quit to the character selection screen and remembering what happened yesterday, I chose other character. I entered the Realm without problems, so I happily quit and tried to enter again with my Sorceress... and of course the game crashed again. This time I made a screenshot, which I am attaching below (or you can see it here: https://puu.sh/yDuS1/f560918e46.png )

Halt
Location : , line #827
Expression: Urecoverable internal error 6f8f78ee

Any idea why is it happening?
Does it always happen, when one finishes Difficulty and tries to join Realm again?
Any idea how to prevent it from happening, so the game doesn't crash and I can keep playing?

 

Now game got broken for me :O
This time I was able to join realm, but after trying to join the chat, the error appeared again:
https://puu.sh/yDvGJ/a0ebdbb66c.png

Another try: I tried to make a game, but I received some "bad image" error and game crashed:
https://puu.sh/yDvHQ/b345c08258.png

I tried once more and again, but now I keep getting 2 errors, whenever I try to join or host the game, no matter which character I use:
error 1 : https://puu.sh/yDvHQ/b345c08258.png
error 2 : https://puu.sh/yDvRp/c82d6273cf.png

So, I should reinstall the game and client? I will try, but why would everything be perfectly fine all the time, then every time I beat the difficulty, things get broken? Never happened to me on any other server on original Battle.Net, so I assumed that maybe it's client related

@Gix I will try doing this, probably tomorrow or day after that, then I will try to beat some difficulty with another character, and I will answer here if it helped or if things changed

Edit: @colder exactly the same as here But if trying to join chat crashes my game an trying to join any game crashes it too, then I don't know, if we can communicate there.

 

Errors are common with any piece of software out there and troubleshooting isn't always precise so you may encounter such odd errors too, out of nowhere.
(...)
Anyhow, the other two errors are definitely a sign that you need to perform a full reinstall of the game so start with that and let us know how it goes.​

Thank you! This gave me an idea, as I had similar situation with other game in past, and looks like I fixed the latter problem in a very easy way, game works again without a need of reinstalling it!
I have the game on external HDD and after the "Unrecoverable internal error", while trying to terminate the game, I unplugged it and plugged it in again. Looks like something went wrong and it was seeing some files, but some of them were not working. The game somehow was launching, but then it was crashing, as it couldn't access some files. Re-attaching it properly fixed it and now I can play again.

The first and the weirdest problem remains unsolved for now though - why the game works fine, then crashes after beating the game difficulty and trying to re-enter the realm?
I will see, if beating the game with some other character will result with the same thing happening. If so, then I will try to actually re-install everything and beat the game on some difficulty again. I will keep you informed, whether this happens again or it gets solved somehow ​