I have yet to find a solution to this error, near as i can tell lowering the graphics detail reduces the occurence but will not get rid of it (tho it is usually only a problem with sieges for me). The following is what i have noticed from my experiences, and the settings i currently use. I have up to date ATI Catalyst drivers for my 4850 512mb.
DirectX = I have found that i dont get these errors with DirectX 7 setting, if you can stomach the change then do it.
Resolution = I play in 1440x900 and tried 1280x960 and didn't notice any change in error regularity
Corpses = I play with it set to 0, which has all but stopped the error for normal battles.
Ragdoll = Again set to 0, after a while you get used to it.
Detail, Textures and character= at full, pride won't let me lower them, but likely would reduce errors.
Grass density = all the way down.
Blood Stains = off, i don't think they look all that great anyway
Shadows = if it has 'shadow' in its description then its off or as low as i can get it.
Dynamic lighting = i still have 'on' but this may change in future
Particle Systems = off, i did until recently have it on, but regularity of error was bugging me (excuse the pun).
AF = Turned it off, would be nice but cant play game with it and i dont care about how crisp the error box appears.....
Faster Water Reflections = On, don't tend to see much water reflections anyway and according to the performance % its better to have it on
Pixel shader = off, honestly don't know how much it affects errors.
Vsync = i have kept on, reduces graphical 'screwups'
max frame rate = i kept on 100, didn't worry about changing it.
AA = Currently on 2x was on 4x (couldn't fight through a siege battle and running out of graphical options to decrease, lowered it from 4x to 2x and was able to finish battle).
Battlesize, smaller= less chance of vertex buffer issues, however with siege battles this seems to be irrelevant as as enemies will keep spawning until there all gone rather than breaking up battle into 'small chunks' like normal battles. I currently have it set to 200.
I have been trying many different mods and each one has had this error at least once (including native). I am also using the Missiles fix haven't noticed anything visually, and cant be sure if its improved stability but it hasn't affected the game adversely so i will keep using it.
The general rule of thumb seems to be that to get rid of the error ( and i don't know if its ATI, the games or Microsoft (explain the latter in a jiffy)) you lower the detail until you are happy with the stability you are getting.
With ATI settings i disabled certain features, seems to be important with a lot of games unfortunately, the way i figure it is that if i let the catalyst control centre to any of its 'adapting', customising or improving then games start to have problems. best i can say is a bit of trail and error in the '3d' settings. Also i don't know about others but sometimes when i get the error i will also get the ('scuse the wording) "ATI drivers had a heart attack but was revived, hoped you saved recently" sign in bottom right. A while back i checked the event viewer, (Right click ATI Control center in the whatzit... bottom right corner) and selected to look at 'Administrative Events' and found that the driver dying often occurred within a minute of 'windows defender' finding something with unknown program (in my case the unknown program had something to do with my catalyst drivers)......
I'm afraid i have no idea what performance or stability is like with Nvidia or any other brands cards, but if your getting the Vertex buffer errors then i'm assuming that lowering details will improve perfomance with those cards as well
I hope that my post helps, as the common rules regarding turning off or reducing ragdolls and corpses didn't work very well for me and it seems for others as well.
If i may make a recommendation regarding further development (via mods or later patches), could there be an option to turn off or reduced timespan for weapons, shields etc that get dropped from the dead, as i believe that this would drastically improve game performance and stability (that and siege battles look a tad... strange.. when theres a couple hundred weapons and shields surrounding the top of the ladder).
