If you have never created a FILTER before in your CoreFtp install, the Filters screen shows only the "FILTER OFF" option and no hint about how to configure the filter currently in use.
The PANEL below the Advanced Site Settings -> Filter -> FILTER OFF drop down box is BLANK. A comment would be helpful.
A CoreFtp comment to CREATE or EDIT the FILTERS is done through the GLOBAL "MANAGE" menu would have been very helpful. If this is documented anywhere, I did not find it before finding the solution. I did spend some time trying to figure this out.