MySQL doesn't connect on CalDAV address

[askytalker]

Baikal version: 0.9.5

Expected behaviour:
Should display all events as CalDav file, when acessing baikal/html/dav.php/calendars/[user]/[calendarname]/

Current behaviour:
Shows message:
Baïkal was not able to establish a connexion to the configured MySQL database (as configured in config/baikal.yaml).

Steps to reproduce:

1. I upgraded from 9.3.3 to 9.3.5, not changing the config file.
2. Then after some days, my calendar stopped working on my phone and on desktop.
3. I copied the backuped "Specific" folder to the new one in /var/www/baikal
4. Everything worked after upgrade.
5. After some days baikal/html/dav.php/calendars/[user]/[calendarname]/ shows message 'Baïkal was not able to establish a connexion to the configured MySQL database (as configured in config/baikal.yaml).'
6. Checked if MySQL database works properly. It does.
7. Checked if MySQL can insert and change tables. It can.
8. Renamed a calendar in the baikal admin interface. It works.
9. Don't know what to do know. Can't access my CalDAV calendars.

[askytalker]

An other question is: Should there have been a .db sql file in the Specific/db/, because it is empty now. I'm using MySQL tables for the calendars.