After installing ARAS Innovator 12 SP9 community edition, I got the HTTP Error 502.5 as I tried to login onto the new instance. First thing I did was checking the prerequisites for ARAS innovator, but everything was ok.
So I started to analyse the underlying problem, and it turned out that the XML file .../OAuthServer/OAuth.config is not a valid XML document.
At line 86, you find "1:" right before the "redirectUri" tag. Please remove this two characters and it will start to work.
Hope this is helpful until this mistake is fixed.