Changed IIS DefaultAppPool's settings as follows:
Net FW: V4.0
managed Pipeline: Integrated
Identity: ApplicationPoolIdentity
Also in web.config, add
<pre lang="HTML">
<system.webserver>
<modules runallmanagedmodulesforallrequests="false" />
<validation validateintegratedmodeconfiguration="false" />
</system.webserver>
The Error 500.23 was gone for one (Asp Web Application) of deployed projects, but for another project (Asp Dile System) in the same IIS folder, got Configuration Error at
<pre lang="HTML">
<authentication mode="Windows" />
I am continuing the debugging on that in this project. Thanks to the reviewers, esp. those who provided comments or solutions feedbacks.