Can not change user default calendar permission

 Hi,

 I am using Exchange 2010 and I am trying to change all users default  calander permissions. I found a good PS scirpt that reads all  mailboxes and changes the permission, but there are few calender which can not be changed.

 I get this error 

The operation couldn't be performed because 'xxxx:\Calendar' couldn't be found.
    + CategoryInfo          : NotSpecified: (0:Int32) [Set-MailboxFolderPermission], ManagementObjectNotFoundException
    + FullyQualifiedErrorId : 2A86E099,Microsoft.Exchange.Management.StoreTasks.SetMailboxFolderPermission

 The calendar exists ok, and I can not see that there is a  language problem

 [PS] C:\get-MailboxRegionalConfiguration -identity xxxx

Identity             Language        DateFormat TimeFormat TimeZone
--------             --------        ---------- ---------- --------
                     en-GB           dd/MM/yyyy HH:mm      Greenwich Standard Time

This here below is my calendar which is ok,

[PS] C:\Desktop>get-MailboxRegionalConfiguration -identity yyyy

Identity             Language        DateFormat TimeFormat TimeZone
--------             --------        ---------- ---------- --------
                     en-GB           dd/MM/yyyy  HH:mm     Greenwich Standard Time

 Any ideas??

Erró