I tried following solutions by which similar issues get resolved
- Changing file formats (UTF-8 BOM to UTF-8)
- Renaming Plugins folder
- Replacing Files which are giving error (On enabling wp-debug)
But in my case final solution was to upgrade the WordPress, or more likely you can say replacing core WordPress files using FTP. I followed this guide for manual upgrade: http://codex.wordpress.org/Updating_WordPress