Well i was looking through the files and it is very different from the normal files in the civ4 assets folder (like the text folber usually the pedia civleaders is where you put them i havent played it yet but it might be why it crashes)
but good job on the artwork that dark mark looks sweet but it would look cooler made out of stars like in the book(or at least i thing it was)
and with the text i know the files are probly ok but it might be harder for the game to read so mabye i could change if that is the case
but i have some suggestions i know you want a bunch of leaders but really harry is the leader of DA and "HE WHO MUST NOT BE NAMED" that is so cool to say but anyways he is the only leader for the DEATH EATERS
same for dumbledore BUT what you did allows for more variations for the gameplay but for scenarios i think it would be best to stick to those.
and for scenarios as soon as this is fixed there could be Books 1-6 with a whole bunch of different civs.
also for great people you could have alot of the leaders you have like sirius black and like you could have air units like the advance guard
Oh yeah you could ask kael for his magic stuff to look at and modify to put in here cause that spell avada kadevra would be a hugly awesome spell but you could only cast it once every 2 turns and Promotions like expelliarmus 1, 2, etc. Where 1 would disable an enemy spellcasters spells from 2 spaces away, 2 would be 4 and stuff like that but that would take serious modding
but good job so far
oh and if you need any info there is this awesome site hp-lexicon.org