It's come to my attention that the AI is sometimes selecting the old Celtic civ. I've made a fix, however modbuddy isn't working properly for me at the moment. For now, please replace the code in RemovesCelts.xml with this:

<GameData>
<Civilizations>
<Update>
<Set Playable="0" />
<Set AIPlayable="0" />
<Where Type="CIVILIZATION_CELTS" />
</Update>
</Civilizations>

</GameData>