C# – ODP.NET error Unable to find the Requested .Net Framework Data Provider

I am trying to develop an ASP.NET MVC 4.0 application using Oracle 11g Express and the .NET 4.0 framework. I can connect to the DB using the ODP.NET provider and can also generate my EDMX against the database. What I can't do is query the underlying DB using entity framework. When instantiating my DbContext using the connectionString Visual Studio generated, I get the following error:

Unable to find the requested .Net Framework Data Provider. It may not be installed

However, it is installed because

1. I can see the dll in the GAC.
2. It is mentioned in machine.config.
3. It is referenced by my project.
4. I actually use it to generate my EDMX from the database.
5. I have verified that I am referencing the correct version (4.112.3.0) everywhere

I am running the code locally on Cassini and my hardware is 32-Bit architecture, so I would assume I would only be able to use 32-Bit DLL's, so it's not an architecture problem.

The specific bit of code is as such:

public class MyContext : ObjectContext, IUnitOfWork
{
    public MyContext() 
    : base(ConfigurationManager
          .ConnectionStrings["OracleEntities"]
          .ConnectionString)//Connectionstring is verified
    {}
}

please help me before I leave everything, grow a beard and go live in the mountains somewhere.

SOLUTION: Since I haven't seen any mention of the solution, I'll mention it here for future generations. Andrei below asked about my connection string format and although I was scheptical, I went and had a look. This is what I saw:

metadata=res://*/OracleModel.csdl|res://*/
OracleModel.ssdl|res://*/
OracleModel.msl;
provider=provider=Oracle.DataAccess.Client;
provider connection string="DATA SOURCE=localhost:1521;
PASSWORD=xxx;PERSIST SECURITY INFO=True;USER ID=xxx

Now, pay special attention to the line

provider=provider=Oracle.DataAccess.Client;

it should, in fact, read

provider=Oracle.DataAccess.Client;

otherwise you're telling EF to use [provider.dll], which isn't a real thing. Also note that it seems that the providerName property of the connectionString element seems to have been overridden or ignored.

UPDATE 2: If this STILL does not help, have a look at machine.config. You should see the following section:

<add name="Oracle Data Provider for .NET" invariant="Oracle.DataAccess.Client" description="Oracle Data Provider for .NET" type="Oracle.DataAccess.Client.OracleClientFactory, Oracle.DataAccess, Version=4.112.3.0, Culture=neutral, PublicKeyToken=89b483f429c47342" />

  <remove invariant="Oracle.DataAccess.Client" />

</DbProviderFactories>

If <remove invariant="Oracle.DataAccess.Client" /> is present, comment it out and try again, otherwise, if it's not there, put it in and try again.