Using browser tools (e.g. the Firefox web console), check headers received with server response to GET www.example.com/administrator/
Expected result
"X-Frame-Options: SAMEORIGIN" is received
Actual result
"X-Frames-Options: SAME-ORIGIN" is received
System information (as much as possible)
PHP 5.3.6 on Apache on Linux
Additional comments
What should be server header "X-Frame-Options: SAMEORIGIN" is sent as "X-Frames-Options: SAME-ORIGIN" on Joomla 2.5.24. (I.e. both, header name AND its value are misspelled.)
Simple fix making RTC