I had the same problem back in October, 3 out of 4 flights on a trip had posted correctly. The 4th flight would not post regardless of my attempts. So I kept submitting, multiple times, and each time telling DL/NW that they were wasting my time and their's as all I wanted were my last flight to post correctly. It eventually happend.... 27 days later. If it takes 30+ times to submit, so be it.