[Users] Webdav, Caldav and Ical

[Michael]

Hello readers,

after a switch from icedove/iceowl to Claws i can't edit or view my
*.ical file. I use the "vCalendar" Plugin (Version: 3.11.1) 

Example: 
It works whit the URL
webcal://fsfe.org/events/events.en.ics (A *.ICS File everybody can read)

It dose't work whit (my!) URL:
https://my.webdav.in-berlin.de/foldername/*.ics

Hint: IN-Berlin, a local DIY ISP, i am only a member, not a maker)

I can "mount" my webdav, e.g. as "davs" to my GNU/Linux Distri. Claws
can't locate thus "local files" ?! 

What must i do to work whit my own *:ics Files? 
Thanks in advance

Michael