The error is caused by Facebook cropping the full URL.  As a result, only the Campaign ID is listed in the URL. Because the full URL is not present, the user will receive an error page.

Alternative Solution: Insert the mailing's browser view URL (found through Link Manager of the content) into a provider that shortens the URL (such as Tinyurl.com, for example).  This will populate an abbreviated URL that you can insert into the Facebook code http://www.facebook.com/sharer.php?u=<shortenedurl>
  • Note: We provide links to third-party websites in an effort to help you resolve your issue. We are not responsible for the information on third-party websites, and we cannot assist with implementing resolutions from these websites.