I am having a problem with HDR where, when I pull out my weapon the lighing gets drastically brighter and stays that way until I restart Oblivion. It only occurs with the one weapon, that I've put in game. I've narrowed down the problem to have something to do with the textures. I placed textures from another weapon I've made (does not have the problem) on the weapon and it resolved it, but I'm not sure why. Alpha channels of the normal maps (of the two weapons) have nearly the same range of grey to black. Materials of both weapons are the same. Has anyone else had this problem when creating new textures or has an idea of how to fix it?

I've narrowed down the problem further. It appears to be the alpha channel that is causing the problem. If I have any shade of grey, or white in the alpha the problem occurs. If I have a completely black alpha channel for the normal map the problem does not happen. I have no idea why.

EDIT: When I take out my weapon near the water on a sandy beach (where I placed it) the problem occurs. I tested in the Arcane university and the problem does not happen there and if I travel out to the same beach with my weapon out the lighting does not get brighter.

It would likely have something to do with your mesh's specular and/or emissive qualities. Oblivion uses these two pieces of data to determine the light a mesh will reflect when HDR is enabled, so having them set to too bright a color can cause issues.

You can check and alter that data in NifSkope.

Well, if Oblivion uses that data, that is. I'm no expert on modeling, but that would be the first place I would look.

Both are set to black. I know that the emissive setting has to do with glow maps. Set it to white to show the glow map fully in game. I'm fairly sure it's the alpha that's doing it although I can't figure out why. Does specular material settings effect the normal maps alpha at all. The alpha affects the shininess of the texture, white is extremely shiny in game and black is it not shiny at all. I'll try messing with the specular and emissive settings.

Edit: Setting both specular and emissive to white has no effect on the problem.

Edit2: I may have solved the problem. I had created the textures in 2048 x 2048 pixel dimensions. I tried shrinking them down to 1024 x 1024 and that has somehow resolved the problem....for now

Edit3: My solution has instantly broken. The problems back.

Edit4: I just tried messing with the specular setting again and it seems to have resolved the problem. I'll see how long it lasts. Emissive and specular must conflict with each other or something because changing them both had no effect

Edit5: Problems back.

I've finally found the source of the problem. For anyone with a similar problem: I'm using 3ds max 2010 32 bit and I was using the niftools plugin for the 2009 version. I just found the 3.5 niftools pre-release plugin. Luckily, it had the 2010 plugin supported. After exporting with the new plugin installed the problem does not occur.