i'm having the same problem with excellent jpgs: recuva can't handle them. the files were photographed last night, with no chances for overwrite by any program. and yet, those files recuva says are "unrecoverable" or "poor" were 99% recovered perfectly.
go figure...
[ a few minutes later ] tried another recovery program (testdisk and photorec) and was able to recover ALL of the files from the partition, including those recuva had marked as "excellent" but was unable to recover... the program uses an extremely primitive dos interface, and it's not for the faint of heart, but it worked first time.