Two things to try for a fix (this bug was introduced with version 1.143). If playing with Steam, from the Launcher click "Configure" then tick "Enable Cheats". This sometimes eases Steam-achievement related crashes (because it disables achievements).
For both Steam and non-Steam versions, open up your Module.ini file found in your Warband installation folder, then "Modules\Native\"
Near the bottom of this file, set disable_moveable_flag_optimization to 1
disable_moveable_flag_optimization = 1
This will definitely correct the issue.
But, as Nikolai indicated, you'll find more comprehensive information and faster responses at forums.taleworlds.com for tech issues (and other discussions).
As for using Warband without Steam (which I would recommend...on the whole it seems more stable), you can download Warband directly from
http://www.taleworlds.com/download.aspx?type=2
From within Steam, you can view your CD/serial key for Warband. If the key is 4x4 (xxxx-xxxx-xxxx-xxxx) you can immediately use that key to activate the version you just downloaded directly from Taleworlds. If they key is 5x5 (there is an extra digit and set of numbers) you may be able to use that key to activate the Taleworlds version, or you may need to use the Taleworlds key converter on their website:
http://www.taleworlds.com/main.aspx?dir=convertserial.aspx