[horde] [kronolith] CalDAV / Webdav/ICS after upgrade to 5.1.0 from 5.0.4

[Nobody is Perfekt]

Hello everyone,

I have installed the last Horde version (Horde 5.1.0 and Kronolith 
4.1.0), and now i cant post events over Thunderbird / Lightning .

Error on Thunderbird: MODIFICATION_FAILED and got to "read-only" mode.

I tested all url from Firefox and they are working.
I think the problem is the posting back ?

but ..

No error nor Infos about on apache log or horde log.
URL are ok, compared with then older Horde installation ...
Any Hints ?

Thanks a lot