Awstat keeps annoying with it's SPAM email to www-data mailbox (that nobody reads.) www-mailbox fills fast to it's 50Mb default limit and stops accepting any more messages. These are the usual messages... Fixing these are burdensome when there are hundreds of domains per server.
Please check that the timezone defined in the file /usr/local/ispconfig/server/lib/config.inc.php matches the timezone of your server.