I just tried again and can't replicate the errors.
While I was importing initially and getting all the errors, I was batch importing a whole bunch of hand history files (all in the same big text file, only separated by a blank line) - horse, stud, omaha hi/lo, plo, etc. - when I've done it this way in the past there were never any errors of this type - PTO would take all the omaha hand histories, PTS would take all the stud, razz, etc., and neither would give errors on the hands of other game types.
For this past test import I imported only 6 horse hands - 2 each of stud, razz and stud8 - and it gave no errors. Is it possible that the errors weren't related to the horse stud-type hands - but rather the mixed in omaha hands that it was attempting to read? In other words, was it the new coding language designed to look for the horse hands that was giving an error when it came across a non-horse type game?