Could you please try using the executable on this link?
http://download.taleworlds.com/mb_warband_1122_with_assertions.zip
After downloading the zip file, you should extract it to the game folder (C:\Program Files\Mount&Blade Warband\) and overwrite mb_warband.exe with the new one.
This will hopefully help us find the reason for crashes. After testing it, please post your comments here or bugs.taleworlds.com