pi4t: Install Shadowkeeper
Open your new save in Shadowkeeper, and your corrupt save in the game

Azorth: So when it comes to save corruption I figure there isn't much that can be done.

Is there at least a good save editor so I could simply skip forward the bits where I can't progress normally via dialogues in the game?

I'm currently back after killing Aec'Letec and I would like to progress to Werewolf Island, is there any save editor software that would allow me to do that at least?

Hickory: There is a (VERY) desperate measure you could try: first BACK UP YOUR SAVE GAMES. Download Near Infinity -- it MUST go inside your install folder, and you must have Java installed -- and run it. Open the 'Save' tab and navigate to the save you want to salvage. Select 'BALDUR.SAV' and then press 'Decompress'. Now highlight 'AR1000.ARE' and press delete. Don't touch anything else and then press 'Compress'. Now select anything else in the left-hand window and you will be prompted to save. Do it, and overwrite. CAVEAT: what you have just done is to remove completely the Ulgoth's Beard record from your saved game. This is why I noted it is a desperate measure. All NPCs who are not removed by scripts will be reset as though you've never met them... Ulgoth's Beard will be as though you've never been. But it will at least allow you to go and speak with Mendas to do the Wearwolf Island quest.

pi4t: You might want to consider turning the difficulty right down, which will let you charge through easily. You can also use cheats to make things easier. Just turn it back to your normal level before you level up if you play on core rules or above, or you'll be getting too many hp.

I'm afraid that afaik there isn't a save editor which can alter what quests you have and haven't done, but you can quite easily use Shadowkeeper to give yourself the items, xp and gold of your other party, and just avoid talking to the quest givers for the quests you didn't do. In effect you'll then have done them.

You'll still need to go through Durlag's to trigger, say, finding Dalton, but as I said above you can use cheats to speed things up. I believe they're enabled by default on the GOG version, but if not then just edit the ini to add cheats=1. Then you can use console commands to speed things up, which you can find in several places online, like here. You may find the move location code particularly useful, as you can go straight to the final level. The code for the area is AR0514, though I'm not sure where exactly in the area it will spawn you. Make sure you pick up the appropriate quests you haven't cashed in before starting!

Then the only thing you'll then be missing is journal entries, which I'm afraid I can't help you with. They aren't that essential, though, as they're only the ones for the done quests, and they'll be wiped if you plan to proceed to BG2 anyway.

So, in summary, you should:
Turn the difficulty down to minimum
Load (and don't overwrite!) the latest save you have without the issues
Pick up the quests that are unfinished in your corrupt save
Use the cheat console to skip to the final area of Durlag's Tower
Complete that area, which shouldn't take too long with the lower difficulty and knowledge of how to solve all the puzzles
Save your game in a new save slot
Install Shadowkeeper
Open your new save in Shadowkeeper, and your corrupt save in the game
Copy the inventory differences, gold and experience into your new save (which may be quicker if you sell items you plan to sell first)
Save in Shadowkeeper, and load in the game, and you should be able to progress as usual

Oh, and don't forget to turn the difficulty back up to your normal level when you're done! If you find that you're having trouble, say with the Durlag's Tower boss, you can edit in the items your corrupt save has at that point to make things easier.

I know it looks complicated, but it shouldn't take all too long: no more than an afternoon, in comparison to the time you'd take going all the way through TotSC again.

Azorth: So I managed to progress to the next part by using a cheat code to spawn Mendas without having to enter his house.

CLUAConsole:CreateCreature("Mendas")

Too bad I don't seem able to spawn Therella to finish Dalton's quest this way. I wish there was a way to spawn any NPC.

I'm playing after the shipwreck, so far things seem to be working fine, let's hope there aren't important small houses to enter.

Thanks for the tip.

Hickory: what version of the game are you playing? I know you said it's vanilla, but which version: CD, GOG... which?

Hickory: The problem with spawning Mendas outside of the house is that when the quest ends, you have to follow his aide inside of the house -- it's where the quest ends (in a fight).

I wouldn't worry about Therella, because you don't get anything worthwhile for that quest.

It's perplexing that you are still getting a crash after resetting Ulgoth's Beard. This is suggesting that your installation itself may be either not patched, or possibly have a corrupted area file -- what version of the game are you playing? I know you said it's vanilla, but which version: CD, GOG... which?

Hickory: Ah, thanks. I missed that.

@Azorth: can I make a suggestion to you? For the purpose of troubleshooting only, create a completely new game, new character and everything. Stats don't matter, this is just to rule something out. Start the game, and don't bother with the tutorial, just get to chapter 1 and then use the console to teleport to Ulgoth's Beard -- AVOID Shandlar at all costs! Use a potion of invisibility (console code POTN10) -- and see if you can go into those houses in a completely fresh game. If you cannot, then something is wrong with your installation.

Azorth: No need for that. I saved the game as soon as I got to Ulgoth's Beard for the first time, and it's working fine in that save. Something happaned to my save after I got transported to Durlag's Tower.

I even tried going back to Therella's house as soon as I got to the tower, and it's crashing too, so it's not the installation.

Hickory: Well that's confusing to me, because you don't get 'transported' to Durlag's Tower. :/

Azorth: What I meant is, aftet you get transported to that ice place when you talk to Shandalar.

Hickory: There is a (VERY) desperate measure you could try: first BACK UP YOUR SAVE GAMES. Download Near Infinity -- it MUST go inside your install folder, and you must have Java installed -- and run it. Open the 'Save' tab and navigate to the save you want to salvage. Select 'BALDUR.SAV' and then press 'Decompress'. Now highlight 'AR1000.ARE' and press delete. Don't touch anything else and then press 'Compress'. Now select anything else in the left-hand window and you will be prompted to save. Do it, and overwrite. CAVEAT: what you have just done is to remove completely the Ulgoth's Beard record from your saved game. This is why I noted it is a desperate measure. All NPCs who are not removed by scripts will be reset as though you've never met them... Ulgoth's Beard will be as though you've never been. But it will at least allow you to go and speak with Mendas to do the Wearwolf Island quest.