I modified 5 characters including carth and bastilia, i modded on them their stats, class, appearance. I also modded some items that they have equipped. i tired modding two amours so that they look like the original and had different properties. instead of the argument/conversation i had a black screen with the kotor pointer. Note i had modified my inventory with KSE
I can't quite think of a solution except "reload" or "try to undo everything", because as far as I know none of that hsould have affected yoru game. I presume you did this on an autosave? I don't think there's a point before that argument when you have Bastila in your party for editing. If you added her with KSE then edited her inventory, that may be the problem.