After copying and pasting some xpages or custom controls, when you try to view your changes in a browser, you're getting an error:
Error 404 HTTP Web Server: Item Not Found Exception
Make sure that either Project\Build Automatically
is enabled in Domino Designer, or rebuild. Project\Clean...
rebuilds your application from scratch, getting rid of any stale data.
The error "Item Not Found Exception" indicates that some required java .class files are not found because they haven't gotten built yet.