Writing into "Program Files (x86)" & "Program Files" and system' directories in general requires administrative privileges since Windows Vista.
I did not think about that.
I can implement a messenger that tells you that the cRPG folder does not exist, and that the user does not have admin permissions to create that folder. Though I am not sure whether that justifies an update on its own. Might wait til another thing comes up.
Unless Elio can be arsed to pack another .zip and upload it and edit his post again
So your only way to allow crpg_update.exe to write into program files is launching it as administrator.
By the way that's the reason why cRPG launcher requires admin privileges.
Another solution: updating it manually
With help of GUI, create on desktop a temporary folder and then choose this folder to update/install cRPG. Or simply copy the cRPG folder from your game to the desktop.
Then you have to replace manually the cRPG folder from "Program Files (x86)\M&BW\Modules\"
You do not have to create a temporary folder.
Just choose the desktop instead of your Warband path. The program will create a new folder called "Modules", and another called "cRPG" inside of it.
So you just grab that modules folder including whatever is in it, and copy it over into your Warband main directory.