CCK Node Reference options not showing "this post can't be referenced."
Nodereference checks that the node is valid before allowing it to save. This check is either a 'standard' check that sees if the node is of the appropriate content type (if you configured the nodereference under the Content types that can be referenced checkboxes); or if you're using Views it can be a 'views' check (if you configured the nodereference under Advanced - Nodes that can be referenced (View)) that sees if the specified node is in the output of the view.