So this obviously won't pertain to everyone, and perhaps this only affects a small group of people that already know this, but regardless I'm writing this just in case someone runs into the same issue I did:

If at any point you were tweaking the fallout_default.ini and, in particular, raised the value of uGridsToLoad to something higher than the default of five ( i.e. uGridsToLoad=9 ), please note you will experience a crash on loading your save games if that value somehow gets changed to something lower than your customized value.

This happened to me with the just released patch. Changing the uGridsToLoad value back to what I had it at, however, resolved the issue.

How so? Steam automatically replaces the .ini files every time you run the launcher? How can you set it back and run the launcher without Steam resetting the damn thing again? Gosh I HATE Steam!

The ini file to change the uGridsToLoad value within is the "Fallout_default.ini" file in "Program Files\Steam\SteamApps\common\fallout new vegas"

Also if you are "stuck" with a larger uGridstoLoad value and would like to revert back to a lower value or the default value of 5, try the following:

1) Start the game with the raised uGridstoLoad value and load your saved game.

2) Alt+Tab back to your desktop, open up the "Fallout_default.ini" file in "Program Files\Steam\SteamApps\common\fallout new vegas", and change the value of uGridsToLoad to the default 5. Save the ini file.

3) Go to the "My Documents\My Games\FalloutNV" folder, Right-click on the "Fallout.ini" file there, and click Properties. In the general tab un-check the "Read-only" Attribute

4) Now open that "My Documents\My Games\FalloutNV\Fallout.ini" file and change the value of uGridsToLoad to the default value of 5. Save the ini file.

5) Alt+Tab back into your game, then press ~ to open up console, and type "refini" (without the quotes) to refresh your ini file. Save your game in a new save slot.

6) Exit out of the game, and then start it back up. Your new save should load with uGridsToLoad at 5 now.

*These instructions adapted from a post by "ibitato" on the guru3d forums originally pertaining to Fallout 3

Does the Fallout_default.ini in my fallout new vegas folder override the settings in the Fallout.ini file located in my my documents? The Fallout.ini file always gets overwritten when you run the launcher, but the Fallout_default.ini doesn't. Is this correct? I'll give your other solution a try a second as well.

Correct. I'm sure someone else could answer this more fully, but in short the values of the My documents Fallout.ini file are derived from Fallout_default.ini file.

If you even move or delete the My documents Fallout.ini file you'll see that it is recreated the next time you load the game.