You probably didn't cross thread the plug. It probably tried to seize up because of either carbon in the threads or maybe the dissimilar metals. I worked for VW for several years and we had the same problem nearly every day. Lots of time we couldn't get the plugs out because they were put in dry. You need some kind of anti-seize on the plug threads. You can get Fel-pro anti-seize at most auto parts stores and it works great. In a pinch graphite will work also. Just remember Aluminum and steel don't always mix and Aluminum always loses.
I fish on the edge and stay out of the middle
99 BassCat Jag w/225 Merc Optimax