Fortiweb400C do not generate Attack report

Hi everybody

I have a FortiWeb-400C 5.38,build0491,150824 and it doesn't generate Attack Reports. Only appears this " No matching log data for this report". I have check all the options in the "Report type" but it always appear empty. But, with the "Event Activity" i have no problems.

I tried to modify the time period but it doesn't matter, the report always say "No matching log data for this report"

Could anybody help?

Best regards

Gonzalo