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Cannot seem to use ConfigurationManager class

Hi Experts,
I don't understand why i get this error. Checking the MSDN documentation, it is supposed to work in .NET 3.5:

Even if i have the using System.Configuration; namespace, it still gives me the error. After doing a bit of research, i found some solutions where others had to manually add to the references of the project to System.Configuration DLL. (In the menubar at the top select Project | Add Referemce, then scroll down (in the .NET tab) to System.Configuration and double click it.).

I can do that and it will compile, the only problem i find is that the DLL i reference is associated with the framework 2.0. Will that create a problem knowing that i work on 3.5 for this project?
using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Text;
using System.Configuration;
namespace ZoafabWin.Business
        private SqlConnection GetConnection()
            return (new SqlConnection(ConfigurationManager.ConnectionStrings["zoafab2005ConnectionString"].ConnectionString));            

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1 Solution
Bob LearnedCommented:
The System.Configuration.dll reference is not normally added to the project, so you need to do that before using System.Configuration.

Göran AnderssonCommented:
You always add references manually. That is the normal way of doing it, and the way that everybody adds references.

The using directive only specifies where the compiler looks for identifiers, it doesn't add any references.

There are some classes in the System.Configuration namespace in the mscorlib.dll, so they are always available, that's why it's possible to specify a usinbg directive for that namespace without a reference to the System.Configuration.dll library. The ConfigurationManager class is in the System.Configuration.dll library, so you have to add a reference to the library to have access to that class.

From what I can tell, there is no new version of System.Configuration.dll in framework 3.5, so it would be normal that the latest version would be 2. Framework 2.0 completely replaced framework 1.1, but framework 3.0 and 3.5 build incrementally on framewok 2.0.

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