Use pluralize to properly inflect the number of errors.

railties/lib/rails/generators/erb/scaffold/templates/_form.html.erb

@@ -1,7 +1,7 @@
 <%%= form_for(@<%= singular_name %>) do |f| %>
   <%% if @<%= singular_name %>.errors.any? %>
   <div id="errorExplanation">
-    <h2>The following errors prohibited this form from being saved:</h2>
+    <h2><%%= pluralize(@<%= singular_name %>.errors.count, "error") %> prohibited this <%= singular_name %> from being saved:</h2>
     <ul>
     <%% @<%= singular_name %>.errors.full_messages.each do |msg| %>
       <li><%%= msg %></li>