>The frustrating part is that it does not consistently happen - 8 or 9 times out of 10 it will work.
>
>I know early on I had a problem running some of the C#/VFP interfaces. Under what secuirty context should the VFP dll be running?
>

I am not sure about the security. I would assume that a security problem would raise an exception. Are you using try/catch and displaying any exceptions back to the web page? Setting trace=true in your aspx page directive is a great debugging tool to learn the sequence that events fire on the page. Use Trace.Write or Trace.Warn to write debugging information to instrument your application.