Is it possible to add a new ship type for the AI to construct?
I tried it with an "Attack Ship2", but this leads to an error message during the AI turn in the game.
It is definately possible. I've done it for many AIs. Try again and be very mindful of spacing and whatnot between lines as that will throw it off.
I have added in about 4 types to my 'experimental' race and it builds them all. Of course I had to give it it's own custom 'AI_Construction' file to insert these ships into it's queue. But so far, no errors.