My sister wants to use (final) Vista's integrated backup feature on her
notebook to backup her data to DVD-RW. Problem is she always gets the
message: "Windows Backup failed. Error: Access denied (0x80070005)"

Looks like backup is denied access to some files even though I stopped all
running applications (which shouldn't be necessary due to Vista's Shadow
Copy).

So I go into Event Viewer which only gives me the same error message like
above and an event ID: 4104. Detail view shows me the same information in XML
format and Event Log Online Help is no help.

Then I find the folder C:\Windows\Logs\WindowsBackup with .ETL files in it
which I can open in Event Viewer. But the only thing they contain are log
events that all look like this: "GUID=dbd33fcd-cfba-5174-7b1a-a59ff2eef057
(No Format Information found)." Again each one with an event ID. The event
IDs are 11, 13, 14, 15, 21, 22, 23, 31, 33, 35, 36. Again, detail view, Event
Log Online Help, and web search turn up nothing.

I don't understand why Microsoft doesn't at least log out the files which
Windows Backup was denied access to. Backup is important for me, but I'm
clueless about what I can do at this point.

Any idea is appreciated. Thanks in advance.

Did you ever get a reply? I'm having the same problem.