Well, the Windows 8.1 has the W7 protection for every folder except the users own folders, and to get around that you have to install the game to your own profile folders, even as an Admin. So install the game to this folder:
C:\Users\<user profile name>\BGII - SoA\ or C:\Users\<user profile name>\Games\BGII - SoA\ or the like, where the <user profile name> -folder is, correct, your own admin accounts user profile name.
Also anti virus programs such as the horrible Comodo Internet Security can set your folders into sandbox mode where no matter what's in them, it has no impact on how the game works as they are mirror folders for the real programs in them. And the only good way to re-enable editing of the files is to remove the whole program.
Edited by The Imp, 06 June 2015 - 03:18 AM.
Yep, Jarno Mikkola. my Mega Mod FAQ. Use of the BWS, and how to use it(scroll down that post a bit).
OK, desert dweller, welcome to the sanity, you are free to search for the limit, it's out there, we drew it in the sand. Ouh, actually it was still snow then.. but anyways.