http://www.serebii.net/emerald/palace.shtml
That table should help. Adamant means it'll try to pick Attack, Defense, and Support moves equally often. Since Bulk Up is your only Defense move, it'll get selected more often than any one of your other three moves, since they're all Attack moves. I'm guessing you also get 'Unable to use its power' fairly often with this guy since you have no Support moves. And Shiny Crobat, giving it all attacking moves would mean it'd be 'unable to use its power' even more often...
To some extent, the Battle Palace needs custom pokemon since good battle natures (like Adamant), aren't necessarily good here. For example, with that moveset, a Hasty nature might be better since it has ++ for Attack, = for Defense, and -- for Support.