sharepoint 2013 master page creating tag

whenever i save custom master page, it creates following tag and getting following error,

tag is 

<%@ Page language="C#" inherits="Microsoft.SharePoint.WebPartPages.WebPartPage, Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>

error is

any idea?

Thanks