Provider error on localhost, when moving from xp to windows 7

Question

I am a developer with xp, vista, 7, and apple air. My app works fine on xp, but on 7 gets:

    "Provider cannot be found. It may not be properly installed" 

with Provider=Microsoft.Jet.OLEDB.4.0 (I use access for devlopment)

Why? - windows 7 did work ok at one time (that is, localhost worked ok, and did not give the above provider error)