unable to drag and add field

hello every one...
i'm using webform 7x3.17... and i'm also installed form builder and webform alternate ui...in that alternate ui i couldn't able to drag a field. but while clicking on that field, the field is added with an error...and if i'm delete a added field means it displays access denied and tels "You are not authorized to access this page.".. But i'm the administrator...pls see the screenshot and help me to solve this... i'm the beginner to drupal...
Thank you...