Every change you make in that config files have no effect on the web application. You have to go the web.config file that is generated once the web application is created.
So edit the web.config file in
C:\inetpub\wwwroot\wss\VirtualDirectories\your port number and modify the parameters you have indicated in that web.config file:
- customErrors mode must be “Off”
- compilation debug must be “true”
- SafeMode CallStack must be “true”
The ‘your port number’ piece of path is the port you assigned when you created the Web Application in the Central Administration