The dreaded area lock out glitch.

[The Dandy]

I hate this thing, let's get that straight right from the off, i hate, hate, hate, hate HATE this stupid glitch!!!!
I don't know how, or why, but when one of my characters progresses to a certain point in his career, and massive amounts of progress has been made with this character, an entire area, fully the size of a mountain (and often located around one) becomes inaccessible.
here's how this works, I go to said area, then, i get a CTD.
if i so much as glance at the loading zone within the area, CTD.
every, single teim.
FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUn to watch me type like this isn't it?
but seriously, this bug has got to be staked through the heart, LIKE NOW!!!!

[Kukkī Monsutā]

I seen this in both Fallout 3 and New Vagas. Both times it was caused by something in the area being a corrupted: a bad Mesh/Texture, or busted Script package for example. Do you have this randomly, or is it the same place every time?

[The Dandy]

randomly, and always when my character progresses to a certain point in the game. like, late levels, tons of stuff discovered late.

[Camper Strike]

You're out of luck. Corrupted spawnpoints aren't so common since the latest FO:NV patches.

Here's a few things you can try, but they're not guaranteed to work:

1 - Go inside a building, sleep/wait for a few days (7 days is the optimal, but you're free to try more), then try to go to the area in question. If it CTDs, repeat the two first steps but save and restart your game before trying to to the area.

2 - Do you have any mods that modify spawnpoints? If so, try disabling them and try again.

3 - Try reloading from previous saves.

I've ran into this bug a few times back when I still played FO:NV. I managed to fix one of them (couldn't approach the northeast area of the map otherwise I'd get a CTD) but had no luck with the others.