Forgetting to compile
The original content of this wiki page has been copied
from the PhoneBook tutorial. It might or might not be
in sync with it at the time you are reading this.
This evergreen even bites old-timers occasionally: if you fix something in your PhoneBook.Domain
project and forget to compile, then of course dbschema.exe
won't notice any of your changes and merrily complain of the same problem until you finally DO rebuild your library.