I’ve been tasked with updating a .NET Framework application to .NET 8. I ran Microsoft’s migration tool, and it seemed to go well, with no errors, but I don’t know if there’s anything else I need to do. Trying to run the application locally for the first time, I’m getting this error:

[]

Program.cs:

using System;
using System.Collections.Generic;

namespace GenericEmail
    {
        class Program
        {
            static void Main(string[] args)
            {
                if (args.Length > 0)
                { 
                    ConfigSettings config = new ConfigSettings();


                //the below will be passed in as parameters
                config.reportType = args[0];
                bool isAdminReport = false;
                bool isTest = true;
                
                if (args.Length > 1)
                {
                    isAdminReport = Convert.ToBoolean(args[1]);
                }

                if (args.Length > 2)
                {
                    isTest = Convert.ToBoolean(args[2]);
                }

                config.isAdminReport = isAdminReport;
                config.isTest = isTest;

                //the below are pulled from config file - specific to reportType param

 -----> THIS IS WHERE THE EXCEPTION IS TRIGGERED-------->  config.emailSubject = System.Configuration.ConfigurationManager.AppSettings["EmailSubject-" + config.reportType];
                    config.adminEmailAddresses = System.Configuration.ConfigurationManager.AppSettings["Admin-" + config.reportType];
                    config.noErrorMessage = System.Configuration.ConfigurationManager.AppSettings["NoError-" + config.reportType];`

Here is App.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=mytoken" requirePermission="false"/>

  </configSections>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8"/>
  </startup>
  <appSettings>

    <add key="TestEmailAddress" value="[email protected]"/>
    <add key="EmailServer" value="smtp.myserver"/>
    <add key="EnableSSL" value="false"/>
    <add key="Port" value="25"/>
    
    <add key="EmailSubject-Validation" value="Account # Errors and Unreconciled Jobs"/>
    <add key="Admin-Validation" value="[email protected]; [email protected];  [email protected]; [email protected]"/>
    <add key="NoError-Validation" value="There are no validation errors to report at this time."/>

    <add key="EmailSubject-Blackout" value="Important: AESOP time entered on blackout date"/>
    <add key="Admin-Blackout" value="[email protected]; [email protected]"/>
    <add key="NoError-Blackout" value="There are no absences on blackout dates to report at this time."/>

    <add key="EmailSubject-FFCRA" value="Authorization required for your absence entry"/>
    <add key="Admin-FFCRA" value="[email protected]; [email protected]"/>
    <add key="NoError-FFCRA" value="There are no FFCRA absences to report at this time."/>
    <add key="Sender-FFCRA" value=" [email protected]"/>

    <add key="EmailSubject-FFCRAReport" value="AESOP FFCRA Absence Report"/>
    <add key="Admin-FFCRAReport" value="[email protected]; [email protected]"/>
    <add key="NoError-FFCRAReport" value="There are no FFCRA absences to report at this time."/>
   
    <add key="ClientSettingsProvider.ServiceUri" value=""/>
  </appSettings>
  <connectionStrings>
    <add name="mu_report_dataEntities" connectionString="metadata=res://*/mu_report_data.csdl|res://*/mu_report_data.ssdl|res://*/mu_report_data.msl;provider=System.Data.SqlClient;provider connection string="data source=myserver;initial catalog=mytable;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework"" providerName="System.Data.EntityClient"/>
  </connectionStrings>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="mssqllocaldb"/>
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer"/>
    </providers>
  </entityFramework>
  <system.web>
    <membership defaultProvider="ClientAuthenticationMembershipProvider">
      <providers>
        <add name="ClientAuthenticationMembershipProvider" type="System.Web.ClientServices.Providers.ClientFormsAuthenticationMembershipProvider, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=mytoken" serviceUri=""/>
      </providers>
    </membership>
    <roleManager defaultProvider="ClientRoleProvider" enabled="true">
      <providers>
        <add name="ClientRoleProvider" type="System.Web.ClientServices.Providers.ClientRoleProvider, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=mytoken" serviceUri="" cacheTimeout="86400"/>
      </providers>
    </roleManager>
  </system.web>
</configuration>

It’s been years since I’ve done any .NET coding and I barely remember anything. Any help is greatly appreciated!