Hi
Did you find any solution to this. I upgraded my server a few weeks back and am tired of this high load. Noted that the find command to delete old php sessions is one of the culprits.
Here are the steps that I did and it worked .. hope they help your case. Please post back what you find.
1) mkdir /var/log/mailman
2) touch /var/log/mailman/error
3) chmod 777 /var/log/mailman/error