When in a sentence I want to use the present perfect of get, I say have/has gotten.
A friend of mine (who is American) corrects me, saying I should use have/has got. From my English classes, I remember that the past participle of get is gotten.
Why does my friend tell me that it is not correct to use have gotten?
If that makes any difference, my friend lives on the east coast, closer to the New England zone.