I slowly get a feeling why playstations and the like are such a success.
Please, open Notepad.
In the menu of Notepad find the option open.
Click it.
Browse to your gamefolder. Usually c:/programs/mount&blade/
It may be different on your pc.
If you found that folder enter the folder modules. It's inside your gamefolder. There you find all the folder for your modules you have installed. Chose the one for 1257AD.
In that folder find modules.ini.
That is the file you want.
Open it.
Now find the line where it says load_mod_resource=skyboxes
replace it with load_resource=skyboxes
Save the file. (it's an option in the menu)
Close notepad.
Then open Explorer (windows key + E should open it). If you don't know what I mean with that search for information on the internet.
Find again your module folder for 1257AD inside the game folder for mount & blade.
Find the folder named 'Data' in the module's folder.
Open it.
Delete the file called 'skyboxes.txt'
Start the game and see if it works now.
Please, try to learn how a pc can be used otherwise it's like you want to read a book but can't read.