Report PDF is Blank with a Shrinked Fortinet logo at the top of Pages

hello Everyone,

as i said I'm facing a problem with Local Report

Local Report is enable, and make a pdf file, but when i try to see the reports, it's empty pages with corrupted Fortinet logo at the top of all pages(2,3 pages).

i have a  FG 90D with FortiOS 5.4.8 running.

it was with version 5.4.6 before and had the same problem, I upgrade it to 5.4.8 but still having the problem.

I tested in different programs and clients and different format, still same problem.

i tried Format Log Disk, Rebooting the Device, Disable \ Enable Disk Logging, Enabling Memory Logging & ... but no luck.

i don't know what causing this problem.

any thoughts?