Unfortunately I am writing to you right now, because I have the same issue.
the installer was blocked upon downloading the Zurich update.
When I chose to install it said there was no internet and that it would use the bgl which were already on the computer, what ever that means.
I found some info in the Chicago forum, but I tried to follow your advice, with no luck.
I will try again today, to download everything again with no active anti virus program... AND with the anti virus ignoring the files you suggested.
I hope it will work, because as of now my sim crashes upon accepting the addon manager and couatl dlls!