Hi Carmine,
Just the contrary, the new distortion correction algorithm implemented in recent versions of the StarAlignment tool is much more capable and accurate than previous versions. The local distortion correction algorithm aims at achieving centipixel registration accuracy. However, it is also more demanding of good star shapes to perform precise PSF measurements, and this may cause problems under less than ideal focusing conditions.
"2-D surface spline" and "thin plate spline" are more or less equivalent terms to describe the registration device used by StarAlignment when distortion correction is enabled (thin plate splines is used more frequently).
If you upload the images that are giving you problems, I'd be glad to take a look to try to help you.