Thank you for your answer. I don’t know, but I disabled the address book in DAVx5, made a sync, then re-enabled the address book and finally a sync, now i can add contacts… I have no explanation, to be continued …

Hi, looks like upgrading to latest version of egroupware 14 fixed the issue.

Ah - you are right - that was the problem! Thanks a lot Best regards Holger

Hi there, I posted the problem to EGroupware as well, but did not get an answer there. I finally chose to swith to another CalDAV-Sync app which seems to work better with EGroupware. Thanks anyway.