kentico upgrade issue from version 10 to 11 with web.config

I upgraded my kentico web application project from version 10 to 11 using upgrade installer and used the codeupgrade utility to detect the code issue and modify them. compiled ok.

I got a message of successful upgrade.

When I accessed my website locally, got the error message below

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 Notification Unknown Handler Not yet determined Error Code 0x80070032 Config Error The configuration section 'appSettings' cannot be read because it is missing a section declaration Config File \?\C:\compass_build\CMS\web.config Requested URL http://localhost:80/ Physical Path
Logon Method Not yet determined Logon User Not yet determined

Config Source: 10: </configSections> 11: <appSettings> 12: <add key="CMSProgrammingLanguage" value="C#" />

Could anyone please assist me to fix the issue, thanks

The following things you need to verify.

1. Dll's version if your site in website mode you need to remove all old Dll's and replace with new one.
2. Need verify the .NET Framework version version is available or not in the system.
3. check the event log whether Kentico upgrade is successful or not because on first run Kentico will updates the database changes and their state will be logged in event log