Failed to find or load the registered .Net Framework Data Provider (VS2005)

I am editing some existing code, and as part of the changes I need to add a column to each of two datasets (.xsd in Visual Studio Solution Explorer).

One worked fine - open the designer, right-click, add column.

The second gives the following error:

"Failed to add column. Failed to find or load the registered .Net Framework Data Provider."

As these are both in the same project, I'm confused as to why this one is failing when the other is not.

The only difference I can think of, is that the one that works is selecting from the database directly (SELECT ... FROM TABLENAME); whereas the one that fails is selecting from a database function (SELECT ... FROM dbo.FunctionName(@param) AS ALIASNAME)

Wherever I've looked, people suggest it's an error with the .settings / .config files; but because one works and one fails, I can't see how this can be an issue with references?

This is in a standard vb project in VS2005, that compiles to a DLL - so it's not asp.net.

--Edit--

Right-click, Preview Data also gives the same error.

--Edit2--

When I try and Add a DataSource, I get the following error:

This SQL Server version (10.50) is not supported.

I have SQL Server 2005, and SQL Server 2008 R2 installed, both with latest service packs.

Solution

I tried two things simultaneously, and one of them worked:

I installed the following patch from Microsoft: https://www.microsoft.com/en-us/download/confirmation.aspx?id=15680
I rearranged my machine.config file (SYSTEMROOT%\Microsoft.NET\Framework\v2.0.50727\CONFIG\machine.config), so that in the DbProviderFactories section the one I am using is at the top of the list.