KERBEROS_V4 rejected as an authentication type & cron

Running as cron, I get error msg in mail: KERBEROS_V4 rejected as an authentication type,
even though the ftp does work. Can anyone explain this? Is there a way to stop it?

cron:
35 6 * * 1-5 ./PSS/pss.sh >> ./PSS/pss.log

script pss.sh:
#!/usr/bin/ksh
DIR=/home/informix/PSS
/usr/kerberos/bin/ftp -v -n << _EOF_
open PSSIPADDR
user testuser testpw
ascii
lcd $DIR
put studentinfo.txt
bye
_EOF_

mail:
Message 3:
From informix@pentapp2.iisd1.lcl Wed Jul 29 06:35:08 2009
Date: Wed, 29 Jul 2009 06:35:04 -0500
From: root@pentapp2.iisd1.lcl (Cron Daemon)
To: informix@pentapp2.iisd1.lcl
Subject: Cron <informix@pentapp2> ./PSS/pss.sh >> ./PSS/pss.log
Content-Type: text/plain; charset=UTF-8
Auto-Submitted: auto-generated
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/home/informix>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=informix>
X-Cron-Env: <USER=informix>

KERBEROS_V4 rejected as an authentication type

---------- Post updated at 09:49 AM ---------- Previous update was at 09:47 AM ----------

BTW, I'm running RedHat 5.3