I get the following error when trying to run Warband on Ubuntu 12.04 LTS:

Running Mount And Blade - Warband
./mb_warband_linux: /lib/i386-linux-gnu/libc.so.6: version `GLIBC_2.16' not found (required by ./libcurl-gnutls.so.4)
./mb_warband_linux: /lib/i386-linux-gnu/libc.so.6: version `GLIBC_2.17' not found (required by ./libcurl-gnutls.so.4)
./mb_warband_linux: /lib/i386-linux-gnu/libc.so.6: version `GLIBC_2.17' not found (required by ./libxkbcommon.so.0)

does anyone have any ideas how to fix this? thanks in advance

Try installing the libc6 package. Open a terminal and use the following commands:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install libc6

from the game page:
Minimum system requirements - Linux: Ubuntu 14.04

12.04 only has libc6 up to version 2.15 AFAIK.

time for an upgrade to 14.04 ;)

Yeah it might be time to upgrade from one LTS to another :) ... at the same the Steam version of Warband works on 12.04 :/ so in general it's possible. I was hoping that GOG Team would make it playable on Pangolin as well...oh well I'll just continue to use the windows partition.