Just to add my voice to those who mention the curious messages:
I 've downloaded and installed the whole latest version on 1.143. Any ideas on how to fix it?
You're right, this error has been reported before (for 3.4). It is the operator: agent_set_division that is not recognized in your game (executable file).
I'm not sure why it happens (for a few players as far as I have seen), but you can try a full re-install of Warband 1.143.
The agent_set_divison operator is used by the Dynamic Groups script.
If a full re-install does not fix your issue with agent_set_division, then I can compile a version that excludes the Dynamic Groups scripting so that the agent_set_division is not used. That would be the only alternative fix for your game.
Edit: OR if perhaps the full version of WB 1.143 is bugged, you could install 1.134 and then do the incremental TW update to WB 1.143. I did the smaller update from 1.134 to 1.143 and do not have this issue.