SharePoint Page Layout Error: Only Content controls are allowed directly in a content page that contains Content controls

The cause is improper case for the control tags in my page layout.  A few contorls used a lower case "c" instead of an uppercase "C" in the word content.  The page layout that had trouble had tags that looked like: instead of .  The specific offending tag is the one associated with the page title (<asp:Content ContentPlaceholderID="PlaceHolderPageTitle"runat="server">).  The solution was as simple as correcting the case of the tag name and all worked well.