“You must specify a value for this required field” error when hidding PlaceHolderPageTitleInTitleArea
 Instead of commenting or deleting the following code
asp:ContentPlaceHolder ID="PlaceHolderPageTitleInTitleArea" runat="server 
use style="display:none;" as follows
asp:Panel style="display:none;"
asp:ContentPlaceHolder ID="PlaceHolderPageTitleInTitleArea" runat="server" /
asp:Panel
 
When customizing SharePoint 2010 MasterPages you often don’t want  certain content placeholders to show up on the page.  You should not  delete or comment these elements out but instead set the visible=”false”   or display:none attribute on the content placeholder.