Magento对成员函数的致命错误调用是什么? 以及如何编辑Controller.php

I've have had a good ole search on here to replicate an error I've been receiving in my Magento 1.9 installation (there are a few related posts, but nothing specific)

With my error logs turned on in index.php I receive the following error, in my browser, when trying to add/edit admin users in the backend:

Fatal error: Call to a member function setData() on a non-object in /hsphere/local/home/my-site-user/my-site/designs/app/code/core/Mage/Adminhtml/controllers/Permissions/UserController.php on line 93

Line 93 is:

->setData('action', $this->getUrl('*/permissions_user/save'));

I would be grateful if anybody could point me in the right direction to solve this issue!

Best wishes

David