"key violation" when trying to import data into MS Access
Perhaps some of the data was successfully imported, and on your subsequent attempts it tries to reimport the whole file, and collides with the existing data?  More generally, are there any records in the target table with which it could be colliding?

If that's not the case, try cutting the file in half.  Can you import the first half?  If so, the problem is in the second half.  Recurse to isolate the problem record(s).