Do you perhaps have some field validation rules set on your fields such as a unique values setting?
A unique values setting could keep additional records with the same value from importing and this would match what you report here.
The only field validations are on primary keys that have nothing to do with the data fields. These are generated automatically.
I unistalled version 11 and installed version 10. Still the same results. By doing imports over and over, I generally pick up a few records with each import. Had there been a field validation stopping the process, then there should not have been any records imported after the first import.
I just solved the mystery and thanks from PhilModJunk who gave me the clue. I had a primary key that somewhere I'd modified and the sequence didn't match the total number of records. When I corrected that error, all imports were uploaded without error.