This error is very common with Outlook and is not anything to worry about. You can remove this by following these steps.
Inside Outlook, do the following:
Navigate to File | Options | Advanced
Scroll down to the send/receive heading
Click on the send/receive button on the right
On the right hand side of the send/receive groups window that opens, click on the Edit button
Un-check the "Get folder unread count for subscribed folders"
Under Received mail items, check the option "User the custom behavior defined below"
In the window below that displays your email folders just select the required folders for your mail account and leave any other not required unchecked.
Click Ok and then exit out of options.
Perform a send/receive to test if it is now working.
