I'm at that city full of ghouls that own their own nuclear reactor, Gecko. I have the Magnetic Whatever Thingy that is needed to repair the reactor, but I cannot access it. Harold, who is the boss of the town, should be supposed to give me access to the reactor, for which I need a Yellow Pass Key (and maybe the Red Pass Key too), but commenting him on my intention does not result in any new dialog line and ends the conversation in a rather sudden way. As my character is supposed to be a good thief, I decided to just steal the Pass Keys from someone at the reactor building and so I did. However, when I approach the yellow door, I don't see any way to use the card. The guard does not have any dialog line to use it and using it over the door does nothing either. Maybe I have missed a card panel or something?

That brings me to my second question. Considering the long tradition of bugs/features in RPGS, should I expect ugly surprises in Fallout 2?, I mean, if I something seems to not work, should I blame it on bugs or should think harder on the solution?

It's probably going to be a mix of bugs and you actually needing to find a solution. The versions of the games here on GOG are fully patched which fixed quite a lot of bugs, but there are still a few that sneak in. You might try the Fallout 2 Unofficial Patch (see the sticky thread called "Fallout 2 MODs") to see if that fixes anything.

I didn't have any problems getting to the reactor when I played, but I probably did things differently than you did, and it was a while ago so I don't remember exactly what happened. Is it possible to use the keycard directly on the door? Sometimes using items in Fallout is a little awkward; I'd recommend grabbing the card from your inventory and try using it on anything nearby, including the door and the guard.

It was sort of my fault at the end. Apparently, the Yellow Pass Key (which you find in a locker) is different from the Yellow Reactor Keycard (which you can rob others). I also managed to found the Red one in another locker.

Thanks!