OTP - Opposite Track Path, means the data is burned from the inside of the disc to the outside on the first layer and then from the outside back to the middle on the second layer.
PTP - Parallel Track Path, means the data is burned inside to outside of disc on first layer and then the same again on the second layer.
(I think)
As for problems I don't really know as all my DL backups have been OTP originals. If your worried try PgcEdit as Lightning suggested above.