Finally we have all updated software including OS :)
=> RHEL 5
=> PHP 5
=> MySQL 5
=> Lighttpd 1.4.15 with AIO
Upgrade went quite smoothly, although few php scripts failed due to changes in PHP version, those are fixed now. Let me know any one need any further assistance or have any problem browsing our site or see Internal server 500 error!
While debugging problem, I’ve noticed that few people running wget or other web page grabber software. Please don’t use these tools. I don’t have time and resources to handle such load.