Develop Reference

"The page cannot be displayed because an internal server error has occurred.""

I am deploying a .Net solution to Azure and am getting the above error when I try to run the page.
I read that System.Web has to be stripped down to this. And that's what I did.
<compilation debug="true" targetFramework="4.7.2" />
<httpRuntime targetFramework="4.7.2" />
The solution works locally. Application Insights does not note any errors. Is there an error log somewhere? I have no idea what error this could be. It could be anything.

(I don't have 50 rep so I can't comment, so I have to post as an answer.)
Enable diagnostics logging and report back with the logs. Should shed some light on the problem.

Try setting custom errors to off in your web.config.
<system.web>
<customErrors mode="Off">
</customErrors>
</system.web>
Reference: customErrors Element (ASP.NET Settings Schema)
Don't forget to turn it back on when you have fixed the issue.

Potentially Dangerous request errors

I am hosting my apllications. They are running under .net version 4.0. Everything is working fine. But lately, i am getting error list "Potentially Dangerous request ...". I searched on the internet and found out have i have to set my web.config like this.
<system.web>
<httpRuntime requestValidationMode="2.0" />
<pages validateRequest="false" />
</system.web>
It it is use then the problem is solved. and my question is how to solve the error without using page validate request set false.
is other way able to solve the problem???

Getting web.config error when publishing my ASP.Net website

I'm trying to publish my first ASP.Net website, but I'm getting this error when I try to visit the homepage.
Unrecognized attribute 'targetFramework'. Note that attribute names
are case-sensitive.
Here's the section of the web.config file it is referencing:
<system.web>
<customErrors mode="Off" />
<compilation debug="true" targetFramework="4.5.2" />
<httpRuntime targetFramework="4.5.2" />
</system.web>
And here's the website itself if you want to see the full error page:
http://connellchamberofcommerce.com/
Is the ASP.Net version (4.5.2) supposed to match the .Net version my host uses or something? As I said, this is my first ASP.Net website and I'm pretty confused by this error.

The version information at the bottom of http://connellchamberofcommerce.com/ indicates that the .net version of app pool is 2.0.50727.5491, where as in your web.config file its 4.5.2. So change the app pool to use 4.0.

Your web.config looks fine to me. My guess would be that you have set the wrong .NET version in the AppPool under which your site is running.
Go to your IIS -> Select your desired AppPool -> Click Basic settings and change the .Net version accordingly.

A potentially dangerous Request.Path value was detected from the client (<)

I first searched for this issue on stack & some other sites & implemented solution in web.config file but still getting the error..
My web.config
<system.web>
<compilation debug="true" strict="false" explicit="true" targetFramework="4.5.2"/>
<httpRuntime requestPathInvalidCharacters="<,>,*,%,&,:,\,?" targetFramework="4.5.2" requestValidationMode="2.0"/>
<customErrors mode="Off"/>
<trust level="Full"/>
<pages validateRequest="false">
<namespaces>
<add namespace="System.Runtime.Serialization"/>
<add namespace="System.ServiceModel"/>
<add namespace="System.ServiceModel.Web"/>
</namespaces>
</pages>
</system.web>
I am trying to get Iframe source values from my db table. It's google map I want to include in my page..

This error signals that you are issuing web request with '<' character, and Asp.Net has some prevention against using potentially malicious characters. You should probably set
<system.web><httpRuntime requestPathInvalidCharacters="" /><pages validateRequest="false" /></system.web>
See also http://www.christophercrooker.com/use-any-characters-you-want-in-your-urls-with-aspnet-4-and-iis
But keep in mind that you are switching off functionality that exists to make it harder for attackers to break your web application. So, if I were you, I would first think if I can change the app to not use forbidden chars in URLs

Displaying Error information in C# Asp.Net with the Web.config?

For some reason I can't see any useful information about my errors even though I Changed the customerrors section of the web.config:
<customErrors mode="RemoteOnly">
</customErrors>
All I want to do is be able to see the normal yellow screen of death that shows what is going wrong.
Ever since I tried to upload this site on my local developer PC's IIS, the application has not shown error information.
Whenever I start debugging the application fails immediatly and says, "Server Error in '/' Application." and gives me a 404 http error and only displays the Version of the .net framework and asp.net version.
*UPDATE:
I'm Running this locally on my development pc.

Set the Mode to Off instead of remote only. MSDN explains the different modes here:
http://msdn.microsoft.com/en-us/library/h0hfz6fc.aspx
If you are in RemoteOnly then it will only show the error if you are running it locally.

<configuration>
<system.web>
<compilation debug="true" targetFramework="4.5" />
<httpRuntime targetFramework="4.5" />
<customErrors mode="" defaultRedirect=""></customErrors>
</system.web>
</configuration>
If you want to set your application level exception should redirect to your custom error page, you can do this by going to global.asax file and write the code for redirection in Application_Error method.
For handling all the exception, you just need to write the code for redirection at catch section. Also you can set custom error page for http errors by passing status code.
<customErrors mode="RemoteOnly" defaultRedirect="~/ErrorPages/Oops.aspx">
<error statusCode="404" redirect="~/ErrorPages/404.aspx" />
</customErrors>
follow this link:https://stackify.com/web-config-customerrors-asp-net/