I have updated DNN from 4.7 to 5.1.2 with no issues, and now I'm trying to update the AD Auth Provider, but I'm kind of guessing how to since there I could find no documentation on upgrading from v1.0 (not a slam, Mike, you are awesome, I just couldn't find any). I've left the old provider in place and I'm trying to install over it to keep the upgrade as low impact as possible. But I receive a Failure just after the step "Starting Installation - Config" then "Creating backup of previous version - web.config" and then I get "Failure Exception - Object reference not set to an instance of an object." and then "Failure Installation Failed - Config." Perhaps my issue is related to yours?

Thanks for the reply, Mike. I tried giving the entire web directory Everyone - Full Control and still get the error. I'll try further.

This issue appears to have been caused by the "location" line in the web.config that prevents inheritance of web.config when installing DNN at the top-level of a site rather than as a virtual directory. I commented the "location" tags (don't forget to comment the </location> closer too!) and the install worked. Then I uncommented them again. That allows the install, though it's still not working and now I'm going to have to run back through the configuration to make sure it works the way I had it for my specific scenario.