SharePoint: List does not exist

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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: http://mysharepoint.domain.com, however you do not have an Alternate Access Mapping for mysharepoint.domain.com.