I am getting a similar error when I delete groups of emails in outlook 2007.
I either get the message about the folder being unavailable or outlook actually crashes.the crashing usually occurs after you do several group deletes.
the other extremely annoying thing, when deleting more than one email at a time, is that it moves the selected email to the very top of the email list rather than the next one up or down.
I am running 11.4.6.9214 build 83 and the server version is 11.4.6 13676 on outlook 2007 sp2.