so an intriguing update.
I created a new Excel 2007 file, and just copied in some data into 3 tabs and changed package to point to this new source.
Now, the error is "The Microsoft Office Access database engine could not find the object '_xlnm._FilterDatabase'...... "
So, it seems, with this ADO connection, when you apply any kind of "filter", i.e. I am dynamically iterating through worksheet tabs, then Excel exposes this hidden object.
Does anyone know of a way, perhaps, to only select "real" tabs within the ADO connection string itself?