VS2019-project is unloaded, csproj <UseIISExpress> was changed somehow, - iis

Question

I had a problem and dell premium support ran some kind of upgrade or re-install of windows 10 while keeping my files in tack.
The next day, I was working on my MVC project in VS and it loaded ok and debugging got my application to the login page, which means it had to successfully read the Entity Framework Context with LINQ type stuff, and all of a sudden my project started having these errors about reading Entity Framework Context, but only in one method.
Then things got worse, I first tried to close VS and reopen VS. But this time, it said my project had been unloaded. I tried the option to reload the project, but now I was getting errors about "the operation could not be completed. the system cannot find the path specified" and errors having to do with not being able to find the current file highlighted at the top of the VS editor.
After looking up the unload issues in forums, I saw a suggestion to call up my Mbsa.csproj and change to false and to True. Then my project loaded ok - but why did this change? it was always false in my previous backups.
Then , when trying to run my project with VS Debugging, I started getting connection messages like these:
1 - C:\MBSSys\Mbsa\Mbsa 2020\Mbsa.csproj : error : The Web Application Project Mbsa is configured to use IIS. The Web server 'http://localhost:51700/' could not be found.
2 -The connection to 'localhost' failed.
Error: ConnectionRefused (0x274d).
System.Net.Sockets.SocketException No connection could be made because the target machine actively refused it 127.0.0.1:51712
3 - 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 BeginRequest
Handler Not yet determined
Error Code 0x80070021
Config Error This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".
Config File \?\D:\MBSSys\Mbsa\Mbsa 2020\web.config
Requested URL http://localhost:51700/
Physical Path D:\MBSSys\Mbsa\Mbsa 2020
Logon Method Not yet determined
Logon User Not yet determined
Config Source:
163: <validation validateIntegratedModeConfiguration="false" />
164: <handlers>
165: <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
4 - Error message:
Server Error in Application "application name"
HTTP Error 500.19 – Internal Server Error
HRESULT: 0x80070021
Description of HRESULT
The requested page cannot be accessed because the related configuration data for the page is invalid.
Cause for HResult code 0x80070021
This problem can occur when the specified portion of the IIS configuration file is locked at a higher configuration level.
Resolution for HResult code 0x80070021
To resolve this problem, unlock the specified section, or do not use it at that level. For more information on configuration locking, see How to Use Locking in IIS 7.0 Configuration.
So I am wondering if anyone else has faced this particular issue,
or, if anyone can give me any appreciated advice here.
Thanks for your time and advice. If you need more clues, just ask.

Answer 1

The seems to happen after installing KB4568831.
https://superuser.com/questions/1575295/windows-updates-kb4568831-kb4562899-break-all-net-applications-hosted-in-iis
I could get rid of the 500.19 errors by manually re-installing some optional windows features that the update apparently removes (see below), but after I got auth-related errors instead. In the end I rolled back KB4568831 to resolve the issue for the time being. Hopefully this gets fixed soon.