Okay, let's see.
1) Are you running on Win10? I read somewhere that the administrator rights are "fake", whatever that means. Probably that you have limited permissions for some files or even sections of your PC, even though you seem to be the administrator. I wouldn't know because I run on Ubuntu, Linux...

Google it please and give us some feedback on that.
2) Another thing: Can you delete anything at all on your PC? Just try to delete something like a text file and see what happens. Probably a stupid idea, but better safe than sorry.
3) Have you installed the game in the default Program Files(x86) folder? If that's the case, then probably you don't have permission to poke in there because of point 1? It's generally good advice to install the game and the mods outside of Program Files(x86).
4) Something that crossed my mind: Would restarting your PC in safe mode, if it exists in Win10, solve the problem? Just an idea, because in safe mode you might be able to delete it.
ALSO: Welcome to the fora!
