You probably have a seperate installation of Python 2.7, which causes the problem. See this thread for more information.
https://forum.unity.com/threads/il2cpp-compile-fails-on-empty-project.352102/#po...
Viewing post in Error when trying to build for web (Unity)
Hey there, thanks for helping, but I found where the problem was, and it was pretty by, the path to my project had an accent in it (the one on my computer user's name) and for some reason Unity didn't want to complie in a folder with a path containing any accent. WHich is wierd, because it built my game for standalone without a hinch. Thank you for helping though, I hope this will help someone else :)