If you take a look at this screenshot http://pelgrim.nu/stats.gif

you'll see that some days are just not processed by Webalizer.
This particular customer has used 74 GB's of datatransfer during the first 20 days according to Webalizer, but the server shows 102 GB datatransfer. 25% difference.

As far as I can see this is the only site on the server that has this problem.

As usual.... I am open for suggestions. ;)

Make sure you have enough disk space (or disk quota) for users running webalizer. I found webalizer will not analyze properly if it is running out of disk space.

See my post in this thread:
http://www.webhostingtalk.com/showthread.php?s=&threadid=21963

Thx Chris. I've made the changes. Now we wait and see... ;)