app/views/shared/_error_messages.html.erb
<% if object.errors.any? %>
<div id="error_explanation">
<div class="callout alert">
The form contains <%= pluralize(object.errors.count, "error") %>.
</div><!-- end .alert -->
<ul>
<% object.errors.full_messages.each do |msg| %>
<li class="error-item"><%= msg %></li>
<% end %>
</ul>
</div><!-- end .error_explanation -->
<% end %>