I had the exact same issue on a MSP-> PDX flight several weeks ago, except that in my case as the GM and FO windows opened the first class seats filled as I sat in coach. If your Delta record shows "Not Eligible" on Delta's website, be prepared not to be considered for an upgrade. I called Delta, who said it was NW problem, and NW, who said it was a DL problem. in the end, a NW agent noted after the fact that DL had transmitted a duplicate record to NW so I was booked twice on the same flight, and she said that the NW system won't process the UG if you have a dupe record.