[kronolith] Caldav and Lightning: Error code: Modification_Failed Description: Status Code: 2147500037, The request cannot be processed. Server Replied with 404

[gimili]

Caldav wouldn't work for me with lighting and I got this error code in 
lightning:  Error code:  Modification_Failed Description:  Status Code:  
2147500037, The request cannot be processed.  Server Replied with 404.  
If I change authentication from Imp to IMAP authentication it seems to 
solve the problem but now I have to login to Imp after Horde.  It may 
have something to do with this: 
http://lists.horde.org/archives/horde/Week-of-Mon-20110509/040745.html

Is this a bug with horde or lightning or am I doing something wrong?  
Any tips appreciated.  Thanks.