keyword not supported data source

This problem can occur when you reference your web.config (or app.config) connection strings by index...

var con = ConfigurationManager.ConnectionStrings[0].ConnectionString;

The zero based connection string is not always the one in your config file as it inherits others by default from further up the stack.

The recommended approaches are to access your connection by name...

var con = ConfigurationManager.ConnectionStrings["MyConnection"].ConnectionString;

or to clear the connnectionStrings element in your config file first...

<connectionStrings>
    <clear/>
    <add name="MyConnection" connectionString="...

What you have is a valid ADO.NET connection string - but it's NOT a valid Entity Framework connection string.

The EF connection string would look something like this:

<connectionStrings> 
  <add name="NorthwindEntities" connectionString=
     "metadata=.\Northwind.csdl|.\Northwind.ssdl|.\Northwind.msl;
      provider=System.Data.SqlClient;
      provider connection string=&quot;Data Source=SERVER\SQL2000;Initial Catalog=Northwind;Integrated Security=True;MultipleActiveResultSets=False&quot;" 
      providerName="System.Data.EntityClient" /> 
</connectionStrings>

You're missing all the metadata= and providerName= elements in your EF connection string...... you basically only have what's contained in the provider connection string part.

Using the EDMX designer should create a valid EF connection string for you, in your web.config or app.config.

Marc

UPDATE: OK, I understand what you're trying to do: you need a second "ADO.NET" connection string just for ASP.NET user / membership database. Your string is OK, but the providerName is wrong - it would have to be "System.Data.SqlClient" - this connection doesn't use ENtity Framework - don't specify the "EntityClient" for it then!

<add name="ASPNETMembership" 
     connectionString="Data Source=MONTGOMERY-DEV\SQLEXPRESS;Initial Catalog=ASPNETDB;Integrated Security=True;" 
     providerName="System.Data.SqlClient" />

If you specify providerName=System.Data.EntityClient ==> Entity Framework connection string (with the metadata= and everything).

If you need and specify providerName=System.Data.SqlClient ==> straight ADO.NET SQL Server connection string without all the EF additions