"HTTP ERROR 500" after QNAP firmware upgrade from 4.2 to 4.3

Almost php/mysql applications like joomla, mantis, drupal, wordpress are not working after firmware update to 4.3.3. The error message is "HTTP ERROR 500".  This is a headache problem since April.

Googled didn't help me, in the end I have to contact QNAP support  . After few round communications, finally the first step worked for me .  Cheers!

Anyway, I am sharing the completed instructions ...

1. login web admin page>control panel>applications>web server >maintenance>restore
2. php.ini>maintenance>restore
3. control panel>applications>sql server>re-initialize database


update to qnote not working with same error message, which turns out my NAS has php5.5 (an application) installed, caused conflict of php. qnote works after I disable php5.5 icon, but my data @ server end are lost.