Here's some troubleshooting tips. I think Justin is absolutely on the right track. The problem is probably in your denyhosts setup. But let's track it down.
You're getting the error originally from logrotate. So run logrotate:
Assuming you get an error, at least you've got a reproducible case. Now let's see if the problem is in logrotate or denyhosts. Let's use the denyhosts command we saw in logrotate:
/etc/init.d/denyhosts restart > /dev/null
If that gives you an error, you're really close to tracking this down. Try taking off the "> /dev/null" from the end of the line to get more information. Post the output here for help.
However, if neither of the above two tricks got you an error, but you're still getting the error from the cron jobs, you've got a problem. Waiting a week between attempts to debug something sucks.
Add another line to your /etc/crontab. Copy the cron.weekly line, and paste it below all the other lines. Then edit it so all the "when" entries are asterisks.
47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
Change that to:
* * * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
Then it will run once a minute all day long, all week long. This is obviously not something you'd want to leave in there, but it can be helpful in troubleshooting.
In cases where you see errors in cron jobs that you don't see when running the scripts from the command-line, it's almost always a difference in your environment. Check the path first.