If you are creating a character for the first time and pull down menus read "NULL" there a few things you need to do to populate these menus.
In the isx console type in, "ogre spell" This will create a export of all usable spells in the character's spell book. It will end up in the Ability_Information folder mentioned above. For assassins it will be called assassin_SpellExport.xml
Close OgreBot and restart it.