I did a clean install to a shared server of 2.6 (Web) with ASP.NET 4.0 selected for the app pool. This was a newly created domain that has had nothing else on it. I was able to login as admin and went to install a new theme and got a 500 error. Now every
page gets a 500 error. I have wiped the entire directory structure and put newly download files in place, yet continue to get the same 500 error. My last attempt I even waited 4 hours to ensure the ASP.NET process restarted.
HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the
page is invalid.
Detailed Error Information
Module IIS Web Core
Handler Not yet determined
Error Code 0x80070032
Config Error The configuration section 'system.web.extensions' cannot be read
because it is missing a section declaration
Config File web.config
Logon Method Not yet determined
Logon User Not yet determined
Jun 29, 2012 at 4:47 AM
Seems to be popular .net 4.0 error with multiple causes and solutions. Check
this thread for example.