wp_create_category and wp_insert_category not working

I get the error while adding the categories using code.
http://i.imgur.com/AIEwq4M.png

These functions are able to work when using the solution provided on this link.
http://stackoverflow.com/questions/12170554/wordpress-error-call-to-undefined-function-in-plugin

This issue was posted on stackoverflow on “Aug 29, 12“. and till today it’s the same.