When third party add-on (icloud) messed up my outlook with unwise synching, I get this error when I use distribution list item:
"The name or distribution list has been deleted and is no longer a valid address book entry. The operation failed. An object could not be found"
(I had recreated the same distribution list from scratch again and thought I had fixed it). Remove the auto-completed item pertaining to the problem from the drop-down auto-complete list.