>I think you should try renaming the configuration and re-installing to see if it clears this up for you.<
Thank you for your suggestion. As I mentioned I wanted to avoid this if possible as it can be time-consuming and wondered if there was any change which installing the extension might have made which I could undo manually (eg editing menus.xml). As it happens I came across a post on another forum which suggested deleting another configuration file:
Surprisingly this did the trick and I could then reinstall the previous version of SecurityAssist. Installing the beta version seemed to cause the problem but it was possibly coincidence - I didn't want to risk it anyway.