[Outlook 2010] Shared calendar : could not be updated

Hello,

I have a problem.

I have an outlook with lot of shared calendar.

Since few days, For 2 of the shared calendar, i got the message "could not be updated", but only for this 2 calendar and only for one user !!

I checked the right and it's ok.

I deleted the shared calendar and add it again -> same problem .

How can I fix this ?

Thanks