this is my code:

OL.MAPIFolder mapiFolder = GetDedicatedFolderForUserID(userID);

if (mapiFolder != null)
{
folderName = mapiFolder.Name;
}

and i get exception:
System.Runtime.InteropServices.COMException (0x8624010F): The
operation failed.
at Microsoft.Office.Interop.Outlook.MAPIFolder.get_Na me()
at
ActionBase.Office.OutlookAddIn.Managers.OutlookFol derManager.GetDedicatedFolderNameForUserID
(Int64 userID)

So, the object is valid. It's not null, so i suppose that it valid.
And why this strange exception occured?, it's happen from time to
time, very seldom, but may occur.

Any ideas??