I found some related topics which shows this problem is common :
How to solve frequent crashes in RTK XI (english pc version)
Romance of the Three Kingdoms XI problem
But there is no solution for the problem!
Then I found this comment in a pirate torrent website :
Urthurian at 2011-09-29 08:42 CET:
I've downloaded this exact torrent from AiTB twice over past two years or so. This is indeed an amazing game and files are clean and beautiful. HOWEVER, there still is an issue about Deng clan flag crash that was never patched by KOEI.
Whenever a character with a name that starts with "Deng" appears on screen upon marching in an army, convoy, navy, etc., there's chance of game crashing in both XP and Vista mode. If it has not, move the screen the hell away from that Deng Sumthin' character when you are about to save. Loading a game while one of "Deng" unit on the screen will literally FAWCK you up unless you are a prudent player who uses more than one Save location. It is mine, and quiet a few others' Theory this is due to "Deng" clans' flag being graphically bugged. Zoom in on one of them units and see the blur yourself.
Also, game itself will randomly crash at totally unexpected times. There is clearly graphic card issue against newer Graphic Cards with this official version yet KOEI has decided not to create a patch for this. Lastly, Save Files rarely becomes corrupted, causing Deja Vu all over again unless you save quiet often. ... there is yet another problem, but just a simple minor glitch regarding Sovereign's picture. It becomes a blur for no apparent reason in the hours into the game then goes away after a while only to return.
I bloody wish someone could create a patch/fix for above issues that has not only occurred to me but others as well(google it when in doubt), for KOEI has become lame and won't update the game over three years.
Even with all these hassles, i give this game 9 out of 10 for being so L33t.
So the problem is with Deng officers!
Any idea how to omit them from the game completely? (for example by doing some hex editor)