I used to have constant problems with the Aux Dict, so I don';t trust it any more. Mine were always corrupting and failing to be found. When I was desperate to revive the aux I think I used to be able to import the text from the aux dict, create a new auxilliary dictionary and then run a spell check, clicking keep on all the words I knew were already correct - after all that's how they got into the original dictionary.
Hope this helps. Ask again if I have not been as clear as I should.
Regards
Tony