i am trying to open a google search inside an iframe. it was working until recently but something happened.
this can be tested here: http://jsfiddle.net/patrioticcow
The X-Frame option is a header sent by the webserver of the page you are trying to embed into the iframe. It basically tells the browser not to allow embedding the page in an iframe. Have a look at https://developer.mozilla.org/en/The_X-FRAME-OPTIONS_response_header for a more detailed description.
Obviously Google does not want you to embed it's search results into an iframe.