Usually I just do
ctrl+H Clsn2: (MUST HAVE COLON!) and replace with Clsn2Default: (AGAIN, MUST HAVE COLON to prevent empty hitboxes or other errors.)
Not really the best way to fix it, but its the only quick and easy way to fix .AIR files for me. If this doesn't seem to work for you, then it was a good enough suggestion.
He who is brave is free! - Lucius Annaeus Seneca