>I created a VFP DLL that does some data collection and manipulation from a VFP database and sends the results to a SQL Server table.
>
>I then created an EXE in .NET that uses the VFP DLL. The .NET class is based on the ServiceProcess.Servicebase class and installed on the target machine as a system service running under an Active Directory account with proper network permissions.

>Why can't I instansiate this DLL this way?

It really sucks debugging this kind of thing. Do you have any code in the Init() of your VFP COM object? I've started pulling any "Init()" type code out of Init and into another method which I explicitly call from .NET to help debug this kind of thing (so that I know at least my COM component is instanciating).

I'd suggest removing the VFP COM component from the project and re-adding it (which should force VS to rebuild the wrapper). Sometimes this clears things up.