To be honest with you, that’s beyond me if it isn’t a coupling error, not sure what exactly that error means
But, there are some other options:
You can try
hf mf fchk --1k -f mfc_default_keys.dic
and you may get lucky and find all the keys that way
or you can try sniffing the keys from the reader, here’s a little more info about that:
double or, you can wait for someone who knows more than me to come by and help us both, which usually doesn’t take too long 
2 Likes