Every time I try to run TES4 LODGen I get this error:

[00:08] Loader: [All Natural - Indoor Weather Filter For Mods.esp] Adding master "Open Cities Resources.esm"
[00:08] Loader: [Open Cities Resources.esm] Loading file
[00:08] Loader: Fatal: The system cannot find the file specified>
[00:08] Loader: finished

Why does it keep trying to load a mod I don't have and never have installed?

Filter mods should not be active. It is trying to load all of that plugins masters. Deactivate it. Filter mods should only be merged or imported.

Edit: In fact, http://sites.google.com/site/oblivionpoinfo/walkthroughs/posting-your-load-order. Use Wrye Bash to post it, and you should have Wrye Bash if you have filter-tagged plugins installed.

Because it's a master of "All Natural - Indoor Weather Filter For Mods.esp"
That mod shouldn't be in your active mod list since it's a filter, with it active Oblivion shouldn't even start...

I'm dumb, I never rebuilt the based patch before running it. Works now, thanks guys.

I always used TES4LodGen as a very simple and effective "missing master"-detector.
Whenever something like this comes up, you're missing a master in your load order and Oblivion most likely won't even start.

Isn't looking for red boxes in Wrye Bash a little faster? haha

Maybe, but starting WB on my laptop took its time, finding the red box also.
And when I already have to rebuilt my LOD, why not using this to check my load order? :angel:

The problem is, with filter mods, going by the red box or by tes4lodgen for "missing master" detection won't work. Filter mods are deliberately engineered in such a way that those methods become misleading for them. Which is of course why the AN filter file specifically says DO NOT ACTIVATE right there in the mod's description field as well as in the readme.