The pre-requisite files that are necessary for a remote SQL 64bit host:

·         Microsoft SQL Server Native Client - sqlncli_x64.msi

·         SQL Server 2005 Management Objects Collection - SQLServer2005_XMO_x64.msi

·         Microsoft ADOMD.NET - SQLServer2005_ADOMD_x64.msi

These files all need to be installed on the Workflow Server host.  I believe that each one is a dependency for the next one down in the list.

I'm getting this same error message using 64-bit Windows Server for ServiceDesk but pointing it back to an offbox 32-bit SQL Server. I found this link to Microsoft's download site to grab the relevant files.

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=d09c1d60-a13c-4479-9b91-9e8b9d835cdc

I had this same error a few weeks ago.  Go to that url posted above.  Look down the list for the Objects collection.  On the Workflow Server install the Objects Collection exe.  Then installed the MSXML 6.0 (located on the same page and the SQL Server Native Client (On the same page).  All of these items are installed by default on the SQL Server so you wont have to install them there.

Microsoft SQL Server 2005 Management Objects Collection

The Management Objects Collection package includes several key elements of the SQL Server 2005 management API, including Analysis Management Objects (AMO), Replication Management Objects (RMO), and SQL Server Management Objects (SMO). Developers and DBAs can use these components to programmatically manage SQL Server 2005.

Note: Microsoft SQL Server 2005 Management Objects Collection requires Microsoft Core XML Services (MSXML) 6.0 and Microsoft SQL Server Native Client, also available on this page.