Cannot open some keynote files
I've got a lot of keynote files for an iBooks Author project. Some have ceased to open. "xxx.key can't be opened for some reason." None of the previous versions can be read.
I've pulled old backups off Time Machine and they won't open.
I've tried the zip renaming trick to no success. Fixing permissions is not possible since El Capitan.
Stuck.
Keynote 6.6