I was getting errors in SharePoint 2010 when trying to run an audit report, but the error message was not helpful. It told me I needed to turn off custom errors in the web.config file, but didn't tell me where that file was located. Fortunately, with the help of the Internet and a blog article by Greg Galipeau, I found the answer.
The file is located here on the web front end servers: C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\web.config
I made the change, ran iisreset /noforce, and SharePoint errors were suddenly much more descriptive.
