everything was fine about my selfoss installation and I was working with it with just little problems.

the only problem i've faced was the "PDO: MySQL server has gone away" error while updating feeds. but this issue takes long just for 1 hour and after that everything gets OK automatically.

but from yesterday (about 27 hours ago) this problem occurs again and its not fixed till now!

I was thinking there is a problem with my MySQL server. but when I checked my server status everything was OK and I checked everything related to MySQL (phpmyadmin, other scripts on my host & ...) and all of them seems working fine!