Private folder does not work

Dear all,I am working with a Domino Client 6.01 CF1 and a Domino server 5.08.

My database has been developped with R5 and works well, but during a transition time we have to keep our server in R5 but upgrade our client with R6.01 and I encount a problem with a folder becoming private on first use.

I have the following error message :

“Noteserror : Index is not to be generated on server” (name of my folder).

I have removed and created a new index several times but it never works.

Any idea ?