AgenDav + Baikal Can't create events

I am having trouble using the app AgenDav.
I installed baikal and AgenDav but I can’t add any events on a calendar. I have a PHP error :

A PHP Error was encountered

Severity: Warning
Message: DateTime::setTimezone() expects parameter 1 to be DateTimeZone, boolean given
Filename: libraries/Dates.php
Line Number: 121

I saw that someone else had the same problem : [RESOLU] Agendav ne peut pas lire les calendriers baïkal

I tried his solution but it didn’t change anything …
Any ideas ?

Same problem here, did anyone have a clue ?