Hey,
thanks for the reply. I was able to downgrade to 2407 on my desktop pc. But the error was still there. I was not able to downgrade to any other version. I got errors when trying. I also tested on my laptop at home on 2408. Also my Laptop had the same error. Calendar entries cerated on the laptop didnt synch with webmail. Contacts and Mail syncs fine!
Today i tested at work. Also OL 2408 is installed there - and everything works fine from work!
So can this be some network issue? I have a firewall and adguard (DNS blocking) running. But the firewall shouldnt block outgoing things.