woohoo ! thank you so much for this quick response. i went to my installed plugins and i saw one there named – wp-post-thumbnail. i deactivated this plugin and the error’s gone.
it seems to have been installed by someone who handled the site in the past. It seems this plugin does the following “WP Post Thumbnail enable bloggers to crop and save post thumbnails without manually copy-n-paste custom field values. Version 0.2 Beta 2 | By Stanley Yeoh”. I think deactivating it wont cause much issues to my site.
