Hi,

I used to face the same problem and the following steps worked in my case:

1. Log in to your reservation at NWA.com using the NW PNR
2. Replace your Flying Blue FF information with that of some other partner airline program, I replaced it with my FFP # on Jet Airways
3. Go Back to My Reservations on NWA.com, log in using the PNR, and change your FFP info. again to your Flying Blue FF number.

It should recognize your FB elite status now.

Do let us know if it works or not.

~Infofreak