Looking at the directory structure, you're using the Basic version. You should check in the Resource directory if actions_mod.brf is present: most of the times 'unable to open' means that Warband can't find that file. Another option is that the file is damaged. But I just had a look at that one, and apparently that file had slipped in the Basic pack: it won't hurt to have it there, but it can also be deleted without any problem, as long as you remove the following line from module.ini:
load_mod_resource = actions_mod