Remove calendar rights disabled users

Hi

How can i remove calendar rights for a user that is disabled. I can see that the user previosly had access to the mailbox since it is listed when running get-mailboxfolderpermission -identity enabled_user:\calendar

When running the cmdlet remove-mailboxfolderpermission i get the following error

There is no existing permission entry found for user: disabled_user
    + CategoryInfo          : NotSpecified: (:) [Remove-MailboxFolderPermission], UserNotFoundInPermissionEntryExcepti
   on
    + FullyQualifiedErrorId : [Server=EX,RequestId=4b23b9d8-2c95-4ea1-acf0-5955746f673f,TimeStamp=2016-10-07 19:06:3
   8] [FailureCategory=Cmdlet-UserNotFoundInPermissionEntryException] 3E35E641,Microsoft.Exchange.Management.StoreTas
  ks.RemoveMailboxFolderPermission
    + PSComputerName        : ex server

thanks

Carlos