OK I figured it out - thanks I found below. I hope it helps others.

QuickBooks Simple Start, the request processor now checks the AuthFlags property during
the call to BeginSession to determine whether your application supports QuickBooks
Simple Start.
For existing applications that aren’t designed for QuickBooks Simple Start, no code
changes are necessary, because by default, AuthFlags is set to support QuickBooks Pro,
Premier, and Enterprise.
However, if you are writing an application that does support QuickBooks Simple Start, you
need to explicitly set AuthFlags to indicate your application’s support of that edition.
Otherwise, if your application attempts to begin a session with QuickBooks Simple Start,
you will get an error when you call BeginSession.

Johnf