kde3.4: calendar on imap folder through kmail problem

Hi
I'm using latest kde3.4 from kde-redhat repository on centos3.4
I'm trying to use calendar stored in a imap folder though kmail.
This feature is great because I have imap mail hosted on the internet 
for free. IMAP also is fast and scalable I think.

I've setup the whole thing, and when I add events or todos, it just says 
'unable to save event ...'. But I can see in the imap folder that the 
event is there.
When restarting kontact, the event were effectively not stored.

Can anyone help?

Does anyone knows a free calendar hosting service that is compatible 
with kdepim? web interface or outlook compatibility is better since I 
don't have kde at home. (only at work)
I know icalx.com, but I find it slow and not scalable.

Thanks