Have you tried installing as administrator or installing using a compatibility mode?
I ended up getting GOG versions just to avoid the hassle. They install and run on my machine wtihout problems (in Win10 and Linux Mint).
Thanks for the response, it eventually finished installing after a lengthy updating process which lasted around 7 minutes or so. Games work great, although in BG2 for some reason every time I launch game I get the same message "since this your first time running game, please configure BG2: Throne of Baal...." . Is there a way to get rid of that annoying message?
Try installing it in a non-default path. I bet where you have it installed, it can't access the file location (Documents and Program Files and Windows all have access restrictions).
You might be able to run it as administrator to allow it to write, too.