I was reminded today that when constructing CAML queries you must use internal names by this wonderful exception:

Exception caught Microsoft.SharePoint.SPException: One or more field types are not installed properly. Go to the list settings page to delete these fields. --->
 System.Runtime.InteropServices.COMException (0x81020014): One or more field types are not installed properly. Go to the list settings page to delete these fields.

It's a pretty ominous message for such a simple issue.