crypt: cannot generate key

[00771g-Lukas]

I am trying to use crypt(1). If I invoke
	cat foo | crypt "abcde"
under sh or ksh, it seems to work fine. However, if I extend the key
by one character, and invoke
	cat foo | crypt "abcdef"
under sh, I get the message
	crypt: cannot generate key
(ksh works ok). Does anyone have an idea what the problem is? TIA
-- 

	John Lukas
	att!ihlpf!lukas
	312-510-6290