When using Microsoft Outlook 2010, you get the following error:
The attempted operation failed. An object could not be found.
This can be caused by a number of things, in my case I had deleted all emails from my inbox, but there was still an email left open in the preview pane. Every time Outlook did a Send / Receive, I would get the attempted operation failed message. This is because Outlook could not find the email associated with the preview pane email displayed (presumeably when it tries to mark the email as read).
The fix for this was to always leave an email in the inbox or turn off the preview pane. As a workaround, you can just change folders then change back to the inbox to clear the email in the preview pane.