Using object viewer I see that:

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\System.dll
has a System.Configuration library

There is also a
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\System.configuration.dll

 After firing up VS2005, I loaded an application that was originally written with 1.1. In this I had a lot of references that uses:

 System.Configuration.ConfigurationSettings.AppSettings[]

 I see the Warning:
 Warning 5 'System.Configuration.ConfigurationSettings.AppSettings' is obsolete: 'This method is obsolete, it has been replaced by System.Configuration!System.Configuration.ConfigurationManager.AppSettings

 However, when trying to use the new ConfigurationManager, it does not display with Intellisense and I gives an error:

 Error 5 The type or namespace name 'ConfigurationManager' does not exist in the namespace 'System.Configuration' (are you missing an assembly reference?)

 I have also tried to reference the .NET 2.0 System.Configuration dll to no avail.

 If I reference the System.configuration dll, then use:
 ConfigurationManager.AppSettings[""]

 I get an error:
 Error 2 The name 'ConfigurationManager' does not exist in the current context

 It looks like the IDE is unable to find the .NET 2.0 assemblies.

 --
 MICHAEL CARR

I had installed the .NET 2.0 Redistributable, then VS2005. I have uninstalled everything and I am going to try install only VS2005 and see what the outcome is.

 After firing up VS2005, I loaded an application that was originally written with 1.1. In this I had a lot of references that uses:

 System.Configuration.ConfigurationSettings.AppSettings[]

 I see the Warning:
 Warning 5 'System.Configuration.ConfigurationSettings.AppSettings' is obsolete: 'This method is obsolete, it has been replaced by System.Configuration!System.Configuration.ConfigurationManager.AppSettings

 However, when trying to use the new ConfigurationManager, it does not display with Intellisense and I gives an error:

 Error 5 The type or namespace name 'ConfigurationManager' does not exist in the namespace 'System.Configuration' (are you missing an assembly reference?)

 I have also tried to reference the .NET 2.0 System.Configuration dll to no avail.

 If I reference the System.configuration dll, then use:
 ConfigurationManager.AppSettings[""]

 I get an error:
 Error 2 The name 'ConfigurationManager' does not exist in the current context

 It looks like the IDE is unable to find the .NET 2.0 assemblies.

 --
 MICHAEL CARR

Hi MICHAEL,

Thanks for your post.

I am not sure what wrong with your project. After adding
System.Configuration.dll, have you added the following using statement?
using System.Configuration;

In my test sample, I added the reference to System.Configuration.dll, then
adding the using System.Configuration;. I can get the "appSettings" section
in app.config with the code below:
private void Form1_Load(object sender, EventArgs e)
{
   // Get the appSettings.
   NameValueCollection appSettings =
        ConfigurationManager.AppSettings;

   // Get the collection enumerator.
   IEnumerator appSettingsEnum =
       appSettings.Keys.GetEnumerator();

   // Loop through the collection and
   // display the appSettings key, value pairs.
   int i = 0;
   Console.WriteLine("App settings.");
   while (appSettingsEnum.MoveNext())
   {
       string key = appSettings.Keys[i];
       Console.WriteLine("Name: {0} Value: {1}",
       key, appSettings[key]);
       i += 1;
   }
}

My testing app.config file is:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
 <configSections>
   <section name="CustomSection"
      type="Samples.Config.CustomSection,
        ConfigurationManager,
        Version=1.0.0.0,
        Culture=neutralPublicKeyToken=null"
        allowDefinition="Everywhere"
        allowExeDefinition="MachineToApplication"
        restartOnExternalChanges="true" />
 </configSections>
 <connectionStrings>
   <add name="ConnStr1"
     connectionString="LocalSqlServer: data source=127.0.0.1;Integrated
Security=SSPI;Initial Catalog=aspnetdb"
     providerName="System.Data.SqlClient" />
   <add name="ConnStr2"
     connectionString="LocalSqlServer: data source=127.0.0.1;Integrated
Security=SSPI;Initial Catalog=aspnetdb"
     providerName="System.Data.SqlClient" />
 </connectionStrings>
 <appSettings>
   <add key="AppSetting0"
     value="Monday, February 28, 2005 1:27:59 PM" />
   <add key="AppSetting1"
     value="Monday, February 28, 2005 1:36:40 PM" />
 </appSettings>
 <CustomSection fileName="default.txt" maxUsers="1000"
    maxIdleTime="00:10:00" />
</configuration>

Hope this helps

Best regards,
Jeffrey Tan
Microsoft Online Partner Support

You need to ensure there is a reference to System.Configuration.dll.  Beyond that, it should work.

Where are you pulling the app setttings from? Your codeBehind, another class, another project, etc.?

 After firing up VS2005, I loaded an application that was originally written with 1.1. In this I had a lot of references that uses:

 System.Configuration.ConfigurationSettings.AppSettings[]

 I see the Warning:
 Warning 5 'System.Configuration.ConfigurationSettings.AppSettings' is obsolete: 'This method is obsolete, it has been replaced by System.Configuration!System.Configuration.ConfigurationManager.AppSettings

 However, when trying to use the new ConfigurationManager, it does not display with Intellisense and I gives an error:

 Error 5 The type or namespace name 'ConfigurationManager' does not exist in the namespace 'System.Configuration' (are you missing an assembly reference?)

 I have also tried to reference the .NET 2.0 System.Configuration dll to no avail.

 If I reference the System.configuration dll, then use:
 ConfigurationManager.AppSettings[""]

 I get an error:
 Error 2 The name 'ConfigurationManager' does not exist in the current context

 It looks like the IDE is unable to find the .NET 2.0 assemblies.

 --
 MICHAEL CARR