If you find the error messages in /etc/httpd/logs/error_log  as follows :-

[Tue Mar 28 04:29:42 2006] [notice] child pid 24546 exit signal File size
limit exceeded (25)

This means that you have a log file that is greater than 2GB in size.

To fix this run the following :

cd /etc/httpd/domlogs
 du -sh * | grep [0-9]G

This should show you the file that is causing issues e.g. example.com.log.

To reset it, but loosing the webstats run

cd /etc/httpd/domlogs
rm example.com.log
touch domain.com.log
/etc/init.d/httpd stop
/etc/init.d/httpd start

Do not use just an Apache restart but a full stop/start to make sure it closes all its old files.