Went to the Gun Runner's fortress to buy a plasma rifle and activate the quest to kill the deathclaws, and the guard is still on the moat, blocking it. I talked to him, but he still won't move. I don't have enough super stimpacks to kill him (only have one), and I've tried killing him with dynamite, but I can't. My last save was a long time ago, so if there's any other way to get across, I'd appreciate it. Thanks :)

If you speak with the guard, he will let you pass. But you can't be too close of him, or you'll block his passage.
Thank god the devs fixed this in Fo2 (by adding the push button!).

The problem is that I'm already in; I looked up a video of someone else gaining entrance to the fortress, and in their video, the guard stepped aside. When I asked him for entrance, it teleported me in, and now he's still guarding the entrance, and his text suggests that I'm still on the outside. I'm wondering if there is any way I can get out without angering the Gun Runners, or if I should just load a adequately earlier save.

Yeah, I searched the web a little bit, and it seems my particular glitch is "special" (hooray). I booted up an earlier save and made up my progress, and now it's fine. Guess that taught me to not just quicksave. I'll mark this as the solution, but almabrds gave some helpful advice, too :) Thanks, guys!

Heh. Not sure I earned it, but thanks.

I keep four saves at all times:

TRAVEL - I save here anytime I'm between locations, like after random encounter battles.

ARRIVAL - I save here first thing whenever my character enters a town.

TOWN ONE - I save here frequently as I do things in a town, and just before I leave.

TOWN TWO - I save here when I'm in a town and I've just done something I really don't want to have to repeat.

Saving is quick and easy enough that it isn't hard to keep this up, and it makes sure I don't have to backtrack too far in case something bad happens.

I know it's too late to help you here, but I just had this happen to me. What had happened was that I had SAVED in the gun runners fortress, and when I loaded the save later the guard had repositioned himself back to the spot on the bridge. In my particular case, I tried talking to him, and when he didn't move I just sort of looked around the island and came back to him. I almost started a combat sequence with him, talked to him one more time with standing off to the right of him (from my perspective) and he moved off the blocking spot allowing me to pass.

I'm not sure that its EXACTLY the same since I wasn't teleported in, but it makes me think it'll go through the same motions so long as you give the guard room to move...

I guess my advice would be to be safe and always save before you enter that area. I've been playing this game since it came out in '97, and the Gun Runners has always been a source of problems. You could very easily get through it without an issue, but it's not uncommon for something to go haywire with the scripting there.

Found a new solution that doesn't lose progress:

on the eastern side of the fort, there is a thin patch of radioactive goop that can be walked over.

it may have rad effects (I was wearing power Armour but Ian suddenly vaporized a few moments after), I reloaded to try again and he made it out alive.

I'll suggest this as a new solution because you don't lose progress if you aren't an OCD saver!