Hi,
I suspect you are missing the wt_month_inc.php file. This is similar to the wt_data_inc.php file. You need Cumulus to process both these files and put them in the correct directory. You must already be processing the wt_data_inc.php as you are getting the other data. Just set up Cumulus to process the other "month" file and put it in the ../data directory.
I think the place to set this up in Cumulus is under Configuration - Internet and then click on the files tab
If it doesnt solve it post back.
Andy