Because of use of FF miles I had 2 separated reservations.

1. RT MSP-ATL 1st Class on FF miles NW code share booked via NW
2. RT ATL-NAS purchased via AMEX points

I also should note that I had my NW PE number in the reservation.

On the return I was flying the say day from NAS-ATL-MSP. Here is what happened when I went to checkin online for NAS-ATL even though in both my NW and DL accounts and on the outbound I was required to re-submit our passport numbers and information. Both DL and NW . accounts have this information for both of us. I think the problem is that I was using my NW account but this should be fixable.

The next problem was frustrating. I checked in for the NAS-ATL flight and then tried to checkin for the ATL-MSP flight. Each either from the DL flight with ticket number or confirmation or via the NW site linked to DL I would get boarding passes for the flight I already checked into NAS-ATL. I finally cleared the IE cache and it worked. I suspect that you are using the name page link for both checkins.

thanks