Update: Looking at the items in the mail, it looks like you have Wrath of the Lich King enchanting materials. Those weren’t intended to be in the game prior to Wrath’s Launch so when they were purged, they were automatically “removed” from the mail. Those items likely will not be recoverable because of that and is what is causing the error.
However, I should be able to delete that mail. I figure we are trying to do that with other folk attempting to transfer, I can offer the same if you wish. Just let me know. 