TMG report shows blank "Top Web Sites"

Hi All,

I am sure why but this used to work but it dont seem to anymore, if we run a report everything shows ok apart from "Top Web Sites" which just shows as a - and 100%, its not list the sites.  If you do normal logging reports you can see the sites ok, as we are a large site and to keep logs to a minimum we only log certain fields ( Client IP, Client Username, Log Date, Log Time, Destination IP, Destination Port, URL ) im not sure why it wont list the top web sites in the reports, any ideas what to check ?

Thanks, Duncan