SharePoint: List does not exist

Problem: When trying to “Add new Item” to a SharePoint 2010 list (document library, task list, etc), and you receive this very helpful error.

Cause: Alternate Access Mappings.  It displays this error message when I cannot resolve the URL.

Solution:  Add the mapping.  Example: You are acessing the site via:, however you do not have an Alternate Access Mapping for