ADO connection failed to create object

[SQLWilts]

Hi,
I have an NT4 box that is using UDL and ADO to connect to an SQL server.
All works well in the staging environment - which is (I thought) identical to production.
However, Production gives the "429 ActiveX component can't create object" - and I'm stumped.
The MDAC reports as the same on both machines (2.8), and as far as I can see, both servers are set up with the same permissions.
The connection strings are identical....

connection string = "Driver={SQL Server};server=myserver;database=mydatabase;uid=username;pwd=password"
connection string = "Data Source=myserver;network library=DBMSSOCN;Initial Catalog=mydatabase, User Id=username;Password=password;"

There are other bits to it, but it is failing on:

Set SQL = Server.CreateObject("ADODB.CONNECTION")

As I said, MDAC checks out, permissions check out, file versions are the same...
Anyone have any idea what else I can check?
Nothing using ADO/UDLs on this machine is working