My requirement is to show a standard VF page into a Custom Visualforce page. I am using apex:iframe with 'src' parameter and the value as relative url to the standard VF page. However it does not give any error at compile time but at the runtime it only shows a blank page. Then I opened the developer console on the browser, it shows an error. That says "Refused to display 'https://ap2.salesforce.com/001' in a frame because it set 'X-Frame-Options' to 'SAMEORIGIN'".
This is my iframe.
<apex:iframe src="https://ap2.salesforce.com/001" scrolling="true"/>
Best Answer
I had a similar issue and the solution was to uncheck
"Enable clickjack protection for customer Visualforce pages with headers disabled"
in Setup > Security Controls > Session Settings